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Calculating pay off for credit card with multiple APRs
The first thing you need to do is look at your terms and conditions of your credit card, or ask your bank, how they will apply the payments.  As Dilip notes in his answer, in the US, they will likely apply the minimum payment to the lower rate balance, and then must apply the rest above the minimum to the higher rate balance.  In other countries, this will vary by law and custom.  Do not assume it will pay off the higher balance, or proportionally, without asking. Let's take the following example. You owe $6000.  $5000 is at 13.5% (normal purchase rate) and $1000 is at 22% (cash advance rate).  If your bank applies payments to both balances proportionally, then a payment of $600 will reduce your purchase balance by $500 and your cash advance balance by $100. The average APR, then, is simply sum of the product of the APR times balance.  So here, (.135*5000 + .225*1000)/6000 = 15%.  This is called a weighted average. If the bank applies the payment differently - such as to the lower rate first, or some specified part to the lower rate and the rest to the higher rate - then this will be misleading if you enter it into a calculator, because your average APR will rise over time as you pay off the purchase balance but don't pay off the cash advance balance, or may decrease if the opposite happens. The weighted average is probably reasonably close in the circumstance that you describe, even if you have rules applying the balance differently, so long as they don't 100% pay down the lower rate - so it may be the simplest option for you in terms of rough calculations (where it's not critical to be correct, just close). One approach using the online calculators that might be better, is to treat these like two separate loans/cards.  Many calculators exist for multiple balances.  Then you can allocate funds differently to the two 'cards'.  This would allow you to see how long you will need until you've paid off the higher balance, for example, although it probably won't perfectly match things - unless you find a site that has this specific option available you probably will have to either live with a small error in your calculations or do the math by hand.