Walmart is rolling out a new iPhone trade in deal that will likely benefit those with older iPhone models. The retail giant says it will double the regular value of your iPhone when you trade it in, but only up to $100.

This means that $200 is the maximum value you'll get if your phone is usually valued at less than $200. If it's above that, you'll get the standard trade-in value.

So, for example, if your phone is worth $100, you'll get $200. If it's worth $123, you'll still get $200 since that's the maximum. The deal is valid Oct. 5 through 18.

Of course, your phone's value always depends on the condition it's in, the color of the phone, the storage capacity, and the carrier.

Through Best Buy, a 32GB iPhone 5 on Verizon's network in good condition is worth $225, while Walmart values it at $150. So in that case, Walmart's deal wouldn't benefit you since the most you can get is $200.

Basically, you'll want to check your specific phone model at a few different websites before jumping on Walmart's deal. If you have an iPhone 4 or 4s, chances are you won't be able to get $200 for it anywhere else, so Walmart's new promotion would be a great deal.

If you do opt for the trade in, you can put that money toward an iPhone 6 on contract with AT&T, Verizon, or Sprint. Walmart sells the iPhone 6 for $179, but if you don't feel like purchasing a new phone you can still get the value for your old phone when you trade it in.