Extra Payment Calculator
An extra $100 per month does not feel like much. But on a high-APR balance, that $100 routinely pulls the payoff in by years and saves four figures in interest. See exactly what your extra payment is worth before you commit the money — the motivation tends to take care of itself once the number is real.
How to use it
- 01.Enter the balance, APR, and current minimum payment for the debt you want to attack. For a multi-debt portfolio, start with the highest-APR debt — that is where the extra payment has the biggest impact.
- 02.Enter the extra amount you can put toward this debt each month. Be realistic; an extra payment you cannot sustain does not actually save you the interest.
- 03.Read the comparison. The output shows months to payoff with and without the extra, along with the dollar interest saved. If the savings number surprises you, that is normal; compounding rewards the extra payment far more than intuition suggests.
- 04.A worked example. Take a $3,500 card balance at 24.99% APR with a $105 monthly payment. Held at exactly $105 per month, the card takes 58 months to clear — nearly five years — and accrues roughly $2,500 of interest, most of it in the early years while the balance is still large.
- 05.Add $100 per month and the picture changes completely. At $205 per month, the payoff drops to 22 months and total interest to about $870. The extra $100 saves three full years of payments and roughly $1,665 of interest. Put differently, the interest you avoid covers more than 16 of the extra payments you made.
- 06.Even half of that helps disproportionately. At $155 per month — a $50 extra — the same card clears in 31 months with about $1,280 of interest, still cutting the timeline by more than two years and the interest bill roughly in half. The relationship is not linear: the first extra dollars you add are the most valuable ones, because they attack the balance while it is largest.
The method, briefly
Extra payments work because credit-card-style debt compounds. Every month, the balance accrues interest at one-twelfth of the APR. The portion of your payment that does not go to interest reduces the principal, which then accrues less interest the next month. An extra payment moves more dollars to principal sooner, and that advantage repeats every remaining month of the schedule, which is why the totals diverge so sharply. There is also an asymmetry worth knowing: extra dollars added early in a payoff are worth more than the same dollars added late, because early on the balance is at its largest and the interest clock is running fastest. The result is often dramatic on high-APR debt. In the worked example above, $100 of extra per month turns a five-year slog into a 22-month plan and cuts the interest bill by roughly two-thirds. The calculator quantifies exactly that trade for your own balance: the months and dollars with the extra payment, without it, and the gap between the two.
Frequently asked questions
Which debt should I add the extra payment to?
On math alone: the highest-APR debt. On psychology: the smallest balance (so you finish it fastest and the visible win sustains motivation). For a hybrid approach, RealiPlan supports avalanche above 20% APR then snowball on the rest as a built-in option.
What if I cannot sustain the extra payment every month?
Inconsistent extra payments still help, but not as much as the calculator shows. The 'with extra payment' result above assumes the extra is paid every single month. If you can only do it some months, the actual interest savings is somewhere between the two scenarios.
Do several small extra payments beat one big monthly one?
Marginally, yes. Most cards accrue interest on your average daily balance, so money applied on day 5 of the cycle saves slightly more than the same money on day 28. The effect is small next to the amount itself, but it is free. RealiPlan supports these as snowflake micro-payments logged on top of your regular plan.
Should I save the extra in an emergency fund first?
If you have no emergency fund and a card has an APR under 8%, save first. If your card APR is above 15%, the interest you avoid by paying down debt typically beats the return on a savings account, even adjusted for the risk of a future emergency. Many users split — half to emergency fund, half to debt — until both have meaningful balances.
Does this work for student loans or mortgages too?
Yes, but the math is less dramatic because of the lower APR. An extra payment on a 6% mortgage saves much less per dollar than an extra payment on a 25% credit card. For most users, attacking credit card debt first is the right call before adding extra to a mortgage.
What is a one-time windfall worth, versus a monthly extra?
A windfall (tax refund, bonus) applied to a high-APR debt can save thousands in interest. The math is exactly the same — every extra dollar removes future interest at the debt's APR. RealiPlan has a dedicated windfall modeling feature on the dashboard that handles one-time payments on top of your regular plan.
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