How paying extra each month pays off your loan sooner
Every payment you make covers that month's interest first, and whatever is left goes toward the balance. In the early years of a loan, interest takes the bigger share. When you add a bit extra on top of your normal payment, that money goes straight to principal. A lower balance means less interest next month, so more of each future payment reduces what you actually owe. The effect builds on itself over time, which is why an extra payment made today is worth far more than the same amount paid years from now.
The mechanism is the same whether you owe a few thousand dollars on a credit card or several hundred thousand on a mortgage. Interest is charged as a percentage of the outstanding balance, so the faster you shrink that balance, the less interest you are charged from then on. Your required payment does not change, but a larger and larger share of it lands on principal each month once you start overpaying, accelerating the whole schedule.
Does an extra payment really make that much difference?
Usually, yes, and often far more than people expect. Interest is charged on whatever balance remains, so paying it down early cuts off months or years of charges at the back end of the loan. Even a small amount extra each month can move the payoff date forward and save a meaningful amount in total interest. The higher your rate and the longer your term, the bigger the difference.
A quick example shows the scale. Take a $25,000 balance at 6.5% with a $450 monthly payment. Adding just $100 a month to that payment typically clears the loan a couple of years early and saves a few thousand dollars in interest you would otherwise have paid. Try changing the rate to 12% in the calculator above and the saving jumps again, because high-rate debt rewards early repayment the most. The numbers update the instant you type, so it costs nothing to test a scenario.
Where to send your extra money first
If you carry more than one debt, the math favours sending spare money to the one with the highest interest rate, an approach often called the avalanche method, because that is where each dollar saves the most. Some people prefer the snowball method, clearing the smallest balance first for a quick psychological win, which can be the better choice if motivation is the thing keeping you on track. Both close debts faster than paying minimums everywhere.
This calculator models one loan at a time, so the simplest way to compare is to run your numbers for each debt and see which extra payment buys the largest interest saving. Whatever order you choose, the principle holds: a fixed monthly payment held steady, plus a regular extra toward principal, almost always beats letting a required payment drift down as the balance falls.
How to read your amortization schedule
The table on this page is an amortization schedule: a month-by-month breakdown of the loan. Each row shows how much of that payment went to interest, how much went to the balance, and what you still owe afterward. Early on, more of each payment goes to interest because the balance is large. As you pay it down, more of every payment chips away at principal. Switch between the year-by-year summary and the full monthly view to see exactly where your money goes.
Reading the schedule is the clearest way to understand why early overpayments matter so much. Look at the split in the first year versus the last: at the start, interest can swallow the majority of each payment, while near the end almost the whole payment reduces principal. An extra payment made in year one removes a high-interest balance that would otherwise have compounded for the entire remaining term, which is why the same dollar does so much less good if you wait.
Things the calculator assumes
To keep the result clear, the tool assumes a fixed interest rate, consistent monthly payments and monthly compounding. That is the standard way to estimate a payoff and is accurate for most fixed-rate installment loans and mortgages. Variable-rate products, daily compounding on some credit cards, fees, and changes in your payment will all nudge the real figures slightly. Use the result as a well-grounded estimate, not a lender quote.
Before committing to a plan, it is worth checking two things with your lender: whether overpayments are applied to principal rather than held as a credit toward future bills, and whether there is any early-repayment charge or annual overpayment cap. Once you know your real numbers, you can put them straight into the calculator and build a payoff plan around figures you trust.
A worked example you can follow by hand
Take the numbers this page starts with: a $25,000 balance at 6.5%, a $450 monthly payment, and $100 extra. The monthly interest rate is 6.5% divided by 12, or about 0.542%. In the first month, interest is $25,000 times 0.00542, which is roughly $135. Of your $450 payment, that $135 covers the interest and the remaining $315 reduces the balance. Add the $100 extra and $415 now comes off the balance in month one instead of $315.
That gap compounds. Because the balance is about $100 lower from the very first month, every later month is charged slightly less interest, so a little more of each payment goes to principal than it otherwise would. Run those exact figures through the calculator above and you will see the loan clear about fourteen months ahead of schedule with over a thousand dollars of interest saved, all from an extra amount most budgets can absorb. The arithmetic is simple enough to check one row at a time in the amortization schedule.
| Extra/month | Payoff time | Interest paid | Time saved | Interest saved |
|---|---|---|---|---|
| $0 (required only) | 5 yr 7 mo | $4,822 | — | — |
| $50 | 4 yr 11 mo | $4,235 | 8 mo | $587 |
| $100 (this page's default) | 4 yr 5 mo | $3,777 | 1 yr 2 mo | $1,045 |
| $150 | 4 yr | $3,411 | 1 yr 7 mo | $1,412 |
| $200 | 3 yr 8 mo | $3,110 | 1 yr 11 mo | $1,712 |
Frequently asked questions
- Should I overpay my loan or invest the money instead?
- That comes down to your interest rate compared to what you would expect to earn by investing, and how much you value a guaranteed outcome. Paying extra is a risk-free return equal to your loan rate. This tool only shows the payoff numbers and is not financial advice.
- Will my lender let me pay extra?
- Most do, but some cap annual overpayments or charge early-repayment fees, especially on fixed-rate deals. Check your agreement before committing to a plan.
- Is a one-off lump sum better than a little extra each month?
- Both cut the balance and reduce the interest that builds on it. A lump sum paid sooner tends to save more than the same total spread out over months, because it lowers the balance earlier. This calculator models a steady monthly extra.
- What is an amortization schedule?
- An amortization schedule is a month-by-month breakdown of a loan. Each row shows how much of that payment went to interest, how much went to the balance, and what you still owe afterward. Early on, more of each payment goes to interest. As the balance falls, more goes to principal.
- How accurate are these numbers?
- The calculation assumes a fixed rate and consistent monthly payments, compounded monthly. Your actual statement may differ a little because of rounding, payment timing, or rate changes. Use these figures as a guide, not a lender quote.
- Is this financial advice?
- No. This tool only shows the payoff math for the numbers you enter. It does not account for your wider finances, and it is not advice. The figures from your lender are the ones that count.