When you’re comparing home loans, the headline interest rate only tells part of the story. While a low interest rate can help you save serious money on your loan, a low-rate loan with hefty fees can eat up these savings in the long run.

This is where a comparison rate comes in. A comparison rate takes into account a home loan’s headline interest rate as well as the accompanying fees and expresses these as a single annual percentage. This is a much better tool for determining the true cost of a home loan.

There’s one major problem with comparison rates, though. The way they’re calculated is light-years away from what you’re likely to experience with your home loan.

In 2003, the Australian government made it mandatory for lenders to display comparison rates in their advertising. The idea was that displaying a uniformly calculated comparison rate would help consumers suss out the cost of the various loan products in the market.

A lot has changed since 2003.

As per the government’s guidelines, advertised comparison rates are all calculated on the same loan amount and term. The problem with this is that house prices have skyrocketed since 2003. Meanwhile, the way advertised comparison rates are calculated hasn’t changed.

Advertised comparison rates are based on a $150,000 loan over a 25-year term. With the median capital-city dwelling price now above $630,000, it’s highly unlikely your home loan is going to fit these criteria.

As we’ll find out below, changing the terms of a loan can have a significant impact on the loan’s comparison rate. Let’s look at three comparison rates, all pulled from advertising by real lenders.

Advertised comparison rates Lender A Comparison Rate: 3.72%

Lender B Comparison Rate: 3.74%

Lender C Comparison Rate: 3.81%

We visited each lender’s website to find out how this comparison rate would change under more realistic borrowing circumstances. Fortunately, by law, lenders must provide you a document known as a Key Facts Sheet when you’re applying for a home loan. This document will give you the comparison rate for your specific borrowing amount and loan term. We entered our own info to generate Key Facts Sheets for each of the lenders.

To get a better picture of how different factors can influence a comparison rate, we generated Key Facts Sheets based upon the median Sydney dwelling value of $880,000 and a 10% deposit, leaving a loan amount of $792,000.

When we entered this information on each lender’s website, the results were surprising.

Actual comparison rates Lender A Comparison Rate: 3.79%

Lender B Comparison Rate: 3.74%

Lender C Comparison Rate: 3.78%

After entering these figures for each lender, we found the lender with the cheapest advertised comparison rate actually became the most expensive. Meanwhile, the lender with the most expensive advertised comparison rate actually became cheaper under these criteria.

While the difference in the comparison rates above might seem insignificant, this small change can add up over the life of your loan. Over the course of a 30-year loan term, the total amount you would pay for Lender A’s product would be $1,328,418.80. The total amount for Lender B would be $1,318,818, and the total amount for Lender C would be $1,324,861.40.The loan with the most expensive advertised comparison rate ends up being $3,557.40 less expensive than the loan with the least expensive advertised comparison rate. Meanwhile, the loan in between the two ends up a whopping $9,600.80 less expensive.

The reasons for this can vary. Some home loans incentivise higher borrowing amounts with lower interest rates. Others might incentivise lower loan-to-value ratios and charge higher rates to borrowers with a smaller deposit. A longer loan term can also add to the total amount of interest you pay.

With this in mind, it pays to generate your own Key Facts Sheet for your expected borrowing amount with lenders you’re considering. The advertised comparison rate can be a helpful tool when you’re considering home loans, but if you don’t take the time to dig a bit deeper, you could end up paying thousands more.

Ready to compare home loan rates? Check out today's rates in the table below