How to calculate a loan amortization schedule if you know your monthly payment
It's relatively easy to produce a loan amortization schedule if you know what the monthly payment on the loan is. Starting in month one, take the total amount of the loan and multiply it by the interest rate on the loan. Then for a loan with monthly repayments, divide the result by 12 to get your monthly interest. Subtract the interest from the total monthly payment, and the remaining amount is what goes toward principal. For month two, do the same thing, except start with the remaining principal balance from month one rather than the original amount of the loan. By the end of the set loan term, your principal should be at zero.
Take a simple example: Say you have a 30-year mortgage for $240,000 at a 5% interest rate that carries a monthly payment of $1,288. In month one, you'd take $240,000 and multiply it by 5% to get $12,000. Divide that by 12, and you'd have $1,000 in interest for your first monthly payment. The remaining $288 goes toward paying down principal.
For month two, your outstanding principal balance is $240,000 minus $288, or $239,712. Multiply that by 5% and divide by 12, and you get a slightly smaller amount -- $998.80 -- going toward interest. Gradually over the ensuing months, less money will go toward interest, and your principal balance will get whittled down faster and faster. By month 360, you owe just $5 in interest, and the remaining $1,283 pays off the balance in full.
Calculating an amortization schedule if you don't know your payment
Sometimes, when you're looking at taking out a loan, all you know is how much you want to borrow and what the rate will be. Knowing the payment can help your mental budgeting when considering if you can afford the debt or not. In that case, the first step will be to figure out what the monthly payment will be. Then you can follow the steps above to calculate the amortization schedule.
There are a couple ways to go about it. The simplest is to use a calculator that gives you the ability to input your loan amount, interest rate, and repayment term. For instance, our mortgage calculator will give you a monthly payment on a home loan. You can also use it to figure out payments for other types of loans simply by changing the terms and removing any estimates for home expenses.
If you're a do-it-yourselfer, you can also use an Excel spreadsheet to come up with the payment. The PMT function gives you the payment based on the interest rate, number of payments, and principal balance for the loan. For instance, to calculate the monthly payment in the example above, you could set an Excel cell to =PMT(5%/12,360,240000). It would give you the $1,288 figure you saw in that example. The 5% is the interest rate, 12 indicates it's a monthly payment, 360 is how many payments for the entire loan term, and 240000 is the principal balance.
Why an amortization schedule can be helpful
There are many ways that you can use the information in a loan amortization schedule. Knowing the total amount of interest you'll pay over the lifetime of a loan is a good incentive to get you to make principal payments early. When you make extra payments that reduce outstanding principal, they also reduce the amount of future payments that have to go toward interest. That's why just a small additional amount paid can have such a huge difference.
To demonstrate, in the example above, say that instead of paying $1,288 in month one, you put an extra $300 toward reducing principal. You might figure that the impact would be to save you $300 on your final payment, or maybe a little bit extra. But thanks to reduced interest, just $300 extra is enough to keep you from making your entire last payment. In other words, $300 now saves you more than $1,300 later.
Armed with this knowledge, you can improve your home finances by strategically paying down your mortgage in ways that have the biggest impact, and while improving your credit score in the process.
Be smart about your loans
Even when your lender gives you a loan amortization schedule, it can be easy just to ignore it in the pile of other documents you have to deal with. But the information on an amortization schedule is crucial to understanding the ins and outs of your loan. By knowing how a schedule gets calculated, you can figure out exactly how valuable it can be to get your debt paid down as quickly as possible.
