You already know that no method of contraception is 100% effective to prevent pregnancy when you're engaging in sexual activity which presents a risk of pregnancy. You probably also know, however, that there are reliable methods which are very effective when used properly, and that if you use contraception correctly and consistently, pregnancy becomes a whole lot less likely. But did you know that by doubling up and using two methods, with almost any combination you use, you can get mighty close to that 100% with many combos?

Hormonal methods of contraception are currently the most effective, reversible methods of birth control with perfect use. But with most of them, we can goof up -- maybe we skipped a couple pills or got a new prescription late, maybe we're not so timely about getting our injections or don't have consistent healthcare to get a new one on time, maybe we didn't realize our patch fell off. Oops. But if we're consistently backing up with a secondary method, even if our primary one fails, we're covered. As well, not everyone can use or wants to use a hormonal method: some of us prefer non-hormonal methods or those are our only safe or affordable options. While they aren't as effective in perfect use, if we add a backup method to the mix, we can be just as protected or even more protected from pregnancy as we could be with a more effective single method.

You'll see that some combinations can increase your level of protection substantially, while with other pairs -- especially where user error is a non-issue, like with an IUD or an implant -- the difference is so slight that backing up is just overkill. Regardless, there is no single combination of any two methods here which would leave you with less than 92% effectiveness, and most combinations will bump you up to over 95% protection. The highest combined methods' typical use effectiveness -- condoms paired with an implant - is 99.99% effective, while the lowest -- withdrawal buddied up with spermicide - is 92.17% effective. But no matter how you slice it, adding a second method always bumps up your protection against unwanted pregnancy.

The Caveats: This is a mathematical application. That doesn't mean it's not accurate -- it is, and I've got the migraine and a pile of paper covered with my chicken scratches to prove it -- but it does mean that these rates are arrived at through math, based on the combined effectiveness rates of single methods, not through specific study or clinical trials of the combined methods. The sources of our efficiency rates for single methods can be found on the Birth Control Bingo pages linked for each method.

In some cases, combining any two or more methods may possibly slightly reduce the effectiveness of one in actual use. For example, because oral contraceptive pills thicken cervical mucus, condoms, when not used with additional lubricant, can be more inclined to break due to increased friction. Using withdrawal with condoms may make it more likely to forget to hold the base of the condom and create a condom slip which may not have been as likely to happen without adding withdrawal to the mix. Without specific study on these things, we can't predict how much it may reduce the effectiveness of one method in those cases nor account for that possibility in the math. However, we have only listed combinations of methods which are safe and sound to use together and make for good mates. For instance, it would not be safe to combine Depo-Provera with another hormonal method. The vaginal effects of combining a ring and spermicides could cause a good deal of vaginal irritation . Using more than one condom is something we know makes condoms less effective, not more. Natural family planning can't be combined with oral contraceptives since a person using oral contraceptives no longer has a natural fertility cycle to chart in the first place.

We've also not done the math for using more than two methods. If you are properly and consistently using two reliable methods of contraception, the risk of pregnancy is incredibly small, and adding a third method is not likely to increase your protection by very much. The difference between a combined method that is 99.8% effective with typical use of both and three methods which are 99.78% effective together, for instance, is so small a statistical difference that adding a third method is likely to just be a needless expense and pain in your butt.

Certainly, if you prefer more than two methods, so long as they don't interfere with one another, you can choose to do that, but we'd also encourage you to evaluate your feelings. If two methods with something like a less than 2% chance of pregnancy in typical use -- and that still allows for room when it comes to user error -- still doesn't leave you feeling safe enough, you might want to consider that you're not comfortable enough with the small amount of risk which will always be a part of sexual activities that can result in pregnancy. It would probably be a good idea in that case to revisit your readiness, and either stick with activities which don't carry those risks, or hold off on heterosex (genital intercourse with an opposite-sex partner) until you're feeling more prepared for some small level of risk. When you're so freaked about the possibility of pregnancy that no amount of birth control feels like enough, it's unlikely that even with four methods, that level of anxiety is not going to leave room for actually enjoying the sex you're having (which is the whole point). Your enjoyment is going to be seriously hindered if you're taking a pill, putting in a diaphragm, having your partner put on a condom, using withdrawal and then taking EC. It's ideal and laudable to be smart and to be safe, but if your contraceptive practices start to feel like you're building a bomb shelter in preparation for a nuclear war every time you have sex, you or your partners are probably better off when it comes to your pleasure and mental health to recognize that you're not up to any risk of pregnancy, even a very statistically unlikely one, and to choose to engage in activities where your risks are far lower or nonexistent.

Listings for each single method are alphabetical. The combinations are listed from most to least effective with typical use, since typical use tends to be the most accurate measure for real people in real -- and frequently imperfect -- life. For more information on any of the single methods listed, just click on the links in their titles.

94% effective alone with perfect use - 86% effective alone with typical use

Cervical Barriers + The Contraceptive Implant = 99.99% effective with perfect use - 99.98% effective with typical use

Cervical Barriers + Intrauterine Devices = 99.99% effective with perfect use - 99.89% effective with typical use

Cervical Barriers + Depo-Provera = 99.98% effective perfect use - 99.4% typical use

Cervical Barriers + Combination OCP ("The Pill") = 99.98% effective with perfect use - 98.7% effective with typical use

Cervical Barriers + The Contraceptive Patch = 99.9% effective with perfect use - 98.88% effective with typical use

Cervical Barriers + Minipills = 99.98% effective with perfect use - 98.6% effective with typical use

Cervical Barriers + Male Condoms = 99.88% effective perfect use - 98.0% effective with typical use

Cervical Barriers + Fertility Awareness = 99.88% effective with perfect use - 97.2% effective with typical use

Cervical Barriers + Female Condoms = 99.7% effective with perfect use - 97% effective with typical use

Cervical Barriers + Emergency Contraception = 99.34% effective with perfect use - 96.5% effective with typical use

Cervical Barriers + Withdrawal = 99.76% effective with perfect use - 96.22% effective with typical use

Spermicides with cervical barriers are not listed because spermicide is supposed to be used with them, so effectiveness rates for barrier methods already include the addition of a spermicide. Since the sponge already contains a spermicide, spermicide was also excluded from combination with the sponge.

99.7% effective alone with perfect use - 91% effective alone with typical use

Combination OCP + Cervical Barriers = 99.98% effective with perfect use - 98.7% effective with typical use

Combination OCP + Male Condoms = 99.99% effective with perfect use - 98.7% effective with typical use

Combination OCP + The Sponge = 99.97%effective with perfect use - 98.7% effective with typical use

Combination OCP + Female Condoms = 99.98% effective with perfect use - 98.1% effective with typical use

Combination OCP + Emergency Contraception* = 99.97% effective with perfect use - 97.7% effective with typical use

Combination OCP + Withdrawal = 99.98% effective with perfect use - 97.6% effective with typical use

Combination OCP + Spermicide = 99.9% effective with perfect use - 97.5% effective with typical use

95% effective with perfect use - 79% effective with typical use

Female Condoms + The Contraceptive Implant = 99.99% effective with perfect use - 99.97% effective with typical use

Female Condoms + Intrauterine Devices = 99.99% effective with perfect use - 99.37% effective with typical use

Female Condoms + Depo-Provera = 99.99% effective with perfect use - 99.2% effective with typical use

Female Condoms + Combination OCP = 99.98% effective with perfect use - 98.1% effective with typical use

Female Condoms + The Contraceptive Patch = 99.9% effective with perfect use - 98.32% effective with typical use

Female Condoms + the Vaginal Ring = 99.98% effective with perfect use - 98.32% effective with typical use

Female Condoms + Minipills = 99.98% effective with perfect use - 97.9% effective with typical use

Female Condoms + Cervical Barriers = 99.7% effective with perfect use - 97% effective with typical use

Female Condoms + the Sponge = 99.55% effective with perfect use - 97.1% effective with typical use

Female Condoms + Fertility Awareness = 99.9% effective with perfect use - 95.0% effective with typical use

Female Condoms + Emergency Contraception = 99.45% effective with perfect use - 94.75% effective with typical use

Female Condoms + Withdrawal = 99.8% effective with perfect use - 94.33% effective with typical use

Female Condoms + Spermicide = 99.1% effective with perfect use - 94.1% effective with typical use

Don't forget!The addition of condoms to any method always carries the joint benefit of both allowing men a part in birth control and greatly reducing the risks of sexually transmitted infections.

98% effective alone with perfect use - 86% effective alone with typical use

Male Condoms + The Contraceptive Implant = 99.99% effective with perfect use - 99.99% effective with typical use

Male Condoms + Intrauterine Devices = 99.99% effective with perfect use - 99.88% effective with typical use

Male Condoms + Depo-Provera = 99.99% effective with perfect use - 99.4% effective with typical use

Male Condoms + Combination OCP = 99.99% effective with perfect use - 98.7% effective with typical use

Male Condoms + The Contraceptive Patch = 99.99% effective with perfect use - 98.9% effective with typical use

Male Condoms + the Vaginal Ring = 99.99% effective with perfect use - 98.9% effective with typical use

Male Condoms + Minipills = 99.99% effective with perfect use - 98.6% effective with typical use

Male Condoms + Cervical Barriers = 99.88% effective perfect use - 98.0% effective with typical use

Male Condoms + the Sponge = 99.8% effective with perfect use - 98.0% effective with typical use

Male Condoms + Fertility Awareness = 99.96% effective with perfect use - 96.6% effective with typical use

Male Condoms + Emergency Contraception = 99.78% effective with perfect use - 96.5% effective with typical use

Male Condoms + Withdrawal = 99.92% effective with perfect use - 96.2% effective with typical use

Male Condoms + Spermicide = 99.7% effective with perfect use - 96.1% effective with typical use

99.9% effective with perfect use - 99.9% effective with typical use

The Contraceptive Implant + Male Condoms = 99.99% effective with perfect use - 99.99% effective with typical use

The Contraceptive Implant + Cervical Barriers = 99.99% effective with perfect use - 99.98% effective with typical use

The Contraceptive Implant + Emergency Contraception*= 99.99% effective with perfect use - 99.98% effective with typical use

The Contraceptive Implant + the Sponge = 99.99% effective with perfect use - 99.98% effective with typical use

The Contraceptive Implant + Female Condoms = 99.99% effective with perfect use - 99.97% effective with typical use

The Contraceptive Implant + Withdrawal = 99.99% effective with perfect use - 99.97% effective with typical use

The Contraceptive Implant + Spermicide = 99.98% effective with perfect use - 99.97% effective with typical use

99% effective with perfect use - 92% effective with typical use

The Contraceptive Patch + Cervical Barriers = 99.98% effective with perfect use - 98.88% effective with typical use

The Contraceptive Patch + Male Condoms = 99.99% effective with perfect use - 98.9% effective with typical use

The Contraceptive Patch + Female Condoms = 99.98% effective with perfect use - 98.32% effective with typical use

The Contraceptive Patch + Emergency Contraception*= 99.97% effective with perfect use - 98% effective with typical use

The Contraceptive Patch + the Sponge = 99.97%effective with perfect use - 98.9% effective with typical use

The Contraceptive Patch + Withdrawal = 99.98% effective with perfect use - 97.84% effective

The Contraceptive Patch + Spermicide = 99.8% effective with perfect use - 97.8% effective with typical use

99.7% effective with perfect use - 97% effective with typical use

Depo-Provera + Cervical Barriers = 99.98% effective perfect use - 99.4% typical use

Depo-Provera + Male Condoms = 99.99% effective with perfect use - 99.4% effective with typical use

Depo-Provera + the Sponge = 99.97%effective with perfect use - 99.4% effective with typical use

Depo-Provera + Female Condoms = 99.99% effective with perfect use - 99.2% effective with typical use

Depo-Provera + Emergency Contraception*= 99.97% effective with perfect use - 99.0% effective with typical use

Depo-Provera + Withdrawal = 99.98% effective with perfect use - 98.9% effective with typical use

Depo-Provera + Spermicide = 99.94% effective with perfect use - 98.9% effective with typical use

98% effective with perfect use - 76% effective with typical use

Fertility Awareness + Cervical Barriers = 99.88% effective with perfect use - 97.2% effective with typical use

Fertility Awareness + Male Condoms = 99.96% effective with perfect use - 96.6% effective with typical use

Fertility Awareness + the Sponge = 99.82% effective with perfect use - 96.6% effective with typical use

Fertility Awareness + Female Condoms = 99.9% effective with perfect use - 95.0% effective with typical use

Fertility Awareness + Emergency Contraception = 99.78% effective with perfect use - 94.0% effective with typical use

Fertility Awareness + Withdrawal = 99.92% effective with perfect use - 93.5% effective with typical use

Fertility Awareness + Spermicide = 99.64% effective with perfect use - 93.3% effective with typical use

99.9% effective with perfect use - 99.2% effective with typical use

Intrauterine Devices + Cervical Barriers = 99.99% effective with perfect use - 99.89% effective with typical use

Intrauterine Devices + Male Condoms = 99.99% effective with perfect use - 99.88% effective with typical use

Intrauterine Devices + The Sponge = 99.99% effective with perfect use - 99.87% effective with typical use

Intrauterine Devices + Female Condoms = 99.99% effective with perfect use - 99.83% effective with typical use

Intrauterine Devices + Emergency Contraception* = 99.99% effective with perfect use - 99.8% effective with typical use

Intrauterine Devices + Withdrawal = 99.99% effective with perfect use - 99.78% effective with typical use

Intrauterine Devices + Spermicide = 99.98% effective with perfect use - 99.77% effective with typical use

99.7% effective with perfect use - 90% effective with typical use

Minipills + Cervical Barriers = 99.98% effective with perfect use - 98.6% effective with typical use

Minipills + Male Condoms = 99.99% effective with perfect use - 98.6% effective with typical use

Minipills + The Sponge = 99.97% effective with perfect use - 98.6% effective with typical use

Minipills + Female Condoms = 99.98% effective with perfect use - 97.9% effective with typical use

Minipills + Emergency Contraception* = 99.97% effective with perfect use - 97.5% effective with typical use

Minipills + Withdrawal = 99.99% effective with perfect use - 97.3% effective with typical use

Minipills + Spermicide = 99.95% effective with perfect use - 97.1% effective with typical use

83% effective with perfect use - 72% effective with typical use

Spermicide + The Contraceptive Implant = 99.98% effective with perfect use - 99.97% effective with typical use

Spermicide + Intrauterine Devices = 99.98% effective with perfect use - 99.77% effective with typical use

Spermicide + Depo-Provera = 99.94% effective with perfect use - 98.9% effective with typical use

Spermicide + Combination OCP = 99.9% effective with perfect use - 97.5% effective with typical use

Spermicide + The Contraceptive Patch = 99.8% effective with perfect use - 97.8% effective with typical use

Spermicide + Minipills = 99.95% effective with perfect use - 97.1% effective with typical use

Spermicide + Male Condoms = 99.7% effective with perfect use - 96.1% effective with typical use

Spermicide + Fertility Awareness = 99.64% effective with perfect use - 93.3% effective with typical use

Spermicide + Female Condoms = 99.1% effective with perfect use - 94.1% effective with typical use

Spermicide + Emergency Contraception = 98.1% effective with perfect use - 93.0% effective with typical use

Spermicide + Withdrawal = 99.3% effective with perfect use - 92.4% effective with typical use

91% effective with perfect use - 86% effective with typical use

The Sponge + The Contraceptive Implant = 99.99% effective with perfect use - 99.98% effective with typical use

The Sponge + Intrauterine Devices = 99.99% effective with perfect use - 99.87% effective with typical use

The Sponge + Depo-Provera = 99.97% effective with perfect use - 99.4% effective with typical use

The Sponge + Combination OCP = 99.97%effective with perfect use - 98.7% effective with typical use

The Sponge + The Contraceptive Patch = 99.97%effective with perfect use - 98.9% effective with typical use

The Sponge + Minipills = 99.97% effective with perfect use - 98.6% effective with typical use

The Sponge + Male Condoms = 99.8% effective with perfect use - 98.0% effective with typical use

The Sponge + Fertility Awareness = 99.82% effective with perfect use - 96.8% effective with typical use

The Sponge + Female Condoms = 99.55% effective with perfect use - 97.1% effective with typical use

The Sponge + Emergency Contraception = 99.01% effective with perfect use - 96.5% effective with typical use

The Sponge + Withdrawal = 99.64% effective with perfect use - 96.2% effective with typical use

99.7% effective with perfect use - 92% effective with typical use

The Vaginal Ring + Male Condoms = 99.99% effective with perfect use - 98.9% effective with typical use

The Vaginal Ring + Female Condoms = 99.98% effective with perfect use - 98.32% effective with typical use

The Vaginal Ring + Emergency Contraception* = 99.97% effective with perfect use - 98% effective with typical use

The Vaginal Ring + Withdrawal = 99.98% effective with perfect use - 97.84% effective with typical use

96% effective with perfect use - 73% effective with typical use

Withdrawal + The Contraceptive Implant = 99.99% effective with perfect use - 99.97% effective with typical use

Withdrawal + Intrauterine Devices = 99.99% effective with perfect use - 99.78% effective with typical use

Withdrawal + Depo-Provera = 99.98% effective with perfect use - 98.9% effective with typical use

Withdrawal + Cervical Barriers = 99.76% effective with perfect use - 96.22% effective with typical use

Withdrawal + Male Condoms = 99.92% effective with perfect use - 96.2% effective with typical use

Withdrawal + Combination OCP = 99.98% effective with perfect use - 97.6% effective with typical use

Withdrawal + The Contraceptive Patch = 99.98% effective with perfect use - 97.84% effective with typical use

Withdrawal + the Vaginal Ring = 99.8% effective with perfect use - 97.84% effective with typical use

Withdrawal + Minipills = 99.99% effective with perfect use - 97.3% effective with typical use

Withdrawal + the Sponge = 99.64% effective with perfect use - 96.2% effective with typical use

Withdrawal + Fertility Awareness = 99.92% effective with perfect use - 93.5% effective with typical use

Withdrawal + Emergency Contraception = 99.56% effective with perfect use - 93.25% effective with typical use

Withdrawal + Spermicide = 99.3% effective with perfect use - 92.4% effective with typical use

* EC is not advised for frequent use while using other hormonal contraceptives, or unless the primary hormonal method was known or strongly suspected to fail. Since the effectiveness rate for emergency contraception is variable, we have used Plan B, and used the most effective rate (89%) as perfect use and the least as typical (75%). We do not list EC as a sole method of contraception because due to the amount of hormones in oral EC, the expense and the perfect use effectiveness rate being lower than all other methods perfect use rates, it is not intended nor designed for use regularly, nor is sole use as a habit something we advise.

Want to know how the math works?

Understanding how we worked out the percentages isn't required in order to make decisions about what contraceptive methods you feel most comfortable with - but for those of you who'd like to know, here you are!

When we're talking about the "mathematical likelihood that something happens", the branch of mathematics we need is probability. The probability that something certain will happen = 1; the probability that something impossible will happen = 0. Anything that is unlikely, possible, or likely has a value between 0 and 1: for example, 0.2, 0.5, or 0.8873. The value of all possible outcomes of one event add up to 1.

As we said above, any time there's intercourse or genital-to-genital contact, there can never be zero risk of pregnancy. Using one or more methods of contraception simply makes the chance of pregnancy much smaller, and as you can see in our figures above, when two methods are used, the chance is very small indeed. So, how did we get those figures? When we're talking about the effectiveness of contraception, there are two possible outcomes: a) the person does not become pregnant - that means the method was effective, and we'll call this "Yes" (for "Yes the method was effective"); or b) the person becomes pregnant - that means the method was not effective, and we'll call this "No" (for "No the method wasn't effective"). When someone's using two methods of contraception, to think about that in probability terms, we need to think of it as a chain of events, where for each method the outcome has to be either "Yes" or "No". So, what are all the different possible chains?

Method 1: Yes and Method 2: Yes (final outcome: no pregnancy)

and Method 2: (final outcome: no pregnancy) Method 1: Yes and Method 2: No (final outcome: no pregnancy)

and Method 2: (final outcome: no pregnancy) Method 1: No and Method 2: Yes (final outcome: no pregnancy)

and Method 2: (final outcome: no pregnancy) Method 1: No and Method 2: No (final outcome: there is a pregnancy)

For the final outcome to be "person does not become pregnant", we only need one method to be effective: that means that the first three chains of events result in effective contraception, while the fourth chain is not effective. What we need to know now is the likelihood - the probability - of each chain happening, which will tell us the probability of each final outcome.

It's possible to work out the probability that two methods together are effective by working out the math for the first three chains: however, that's fiddly, complex and error-prone (no thanks!). It's much simpler to work out the probability that none of the methods will be effective just by working out the math for the final chain.

Let's work through an example.

We know from studies that outside ("male") condoms are 86% effective with typical use and the combined pill is 91% effective with typical use. So, how effective can we mathematically expect them to be when used together, with typical use?

Convert the percentages into probabilities (a number from 0 to 1): 86/100 = 0.86 ; 91/100 = 0.91

Use these to find the probability that each method individually is not effective: 1 - 0.86 = 0.14 ; 1 - 0.91 = 0.09

effective: 1 - 0.86 = 0.14 ; 1 - 0.91 = 0.09 To work out the probability of both events happening (Condom: No and Combined Pill: No ), we multiply the probabilities together: 0.14 x 0.09 = 0.0126

and Combined Pill: ), we multiply the probabilities together: 0.14 x 0.09 = 0.0126 So, the probability of the two methods together being effective is 1 - 0.0126 = 0.9874

Converting back to a percentage: 0.9874 x 100 = 98.74%

Rounding to the nearest one decimal place (because it isn't sensible to keep many more than we started with): 98.7%

If you want to work out the effectiveness of three methods for yourself, you can! Before you do, make sure that the methods you're thinking about can be used together - check out the pairings above if you're unsure.

For example: you want to add spermicide to the example we just looked at? Spermicide by itself is 72% effective with typical use.

There's only one possible chain of events which results in the final contraceptive outcome not being effective: Condom: No and Combined Pill: No and Spermicide: No .

and Combined Pill: and Spermicide: . Convert the percentages into probabilities: 86/100 = 0.86; 91/100 = 0.91; 72/100 = 0.72

The probability that each method individually is not effective: 1 - 0.86 = 0.14; 1 - 0.91 = 0.09; 1 - 0.72 = 0.28

effective: 1 - 0.86 = 0.14; 1 - 0.91 = 0.09; 1 - 0.72 = 0.28 To work out the probability of all of those happening, multiply them together: 0.14 x 0.09 x 0.28 = 0.003528

So, the probability of any or all of the three methods being effective is 1 - 0.003528 = 0.996472

Converting to a percentage: 0.99652 x 100 = 99.6472%

Rounding to the nearest one decimal place: 99.6%

Special thanks to Scarleteen volunteer Courtenay for the math formula and her assistance! Updated math with updated single-method rates, math explanation and examples by Redskies. Article illustration by Mark Price.