Snowball Payment Schedule Calculator

A snowball payment schedule calculator shows how a debt payoff plan can progress when you pay the minimum due on each debt and direct extra money to the smallest balance. Enter each balance, interest rate, minimum payment, and your monthly debt budget to estimate the payment order and payoff timeline; the schedule depends on rates and payment rules that can change.

Formula

This single-debt calculator estimates the time and amount needed to repay the current smallest balance under a fixed monthly payment. It is a simplified first-stage view of a snowball plan, not a full multi-debt schedule. It assumes the minimum payment remains fixed and that all of the extra monthly amount goes to this debt.

• Monthly rate, r = APR ÷ 1,200.
• Estimated months, n = round up [−ln(1 − r × balance ÷ payment) ÷ ln(1 + r)].
• Estimated amount paid = monthly payment × n.
• Estimated interest = estimated amount paid − starting balance.

Balance is the principal owed in dollars; APR is the annual percentage rate entered as a percent; r is the monthly rate as a decimal; and payment is the minimum payment plus the extra amount, in dollars per month. The months result rounds up to a whole payment period. This formula models a level payment at the end of each month. The calculator does not model a creditor recalculating minimums as the balance falls.

Worked Example

Using the defaults, the debt balance is $1,000, APR is 18%, the minimum payment is $50, and the extra amount is $200. The modeled monthly payment is therefore $250, and the monthly rate is 18 ÷ 1,200 = 0.015.

1. Find the payment ratio: 0.015 × $1,000 ÷ $250 = 0.06.
2. Apply the payoff equation: −ln(1 − 0.06) ÷ ln(1.015) = approximately 4.15 months.
3. Round up to a whole payment period: 5 months.
4. Estimated total paid: $250 × 5 = $1,250.
5. Estimated interest: $1,250 − $1,000 = $250.

The estimate treats all five payments as $250. In an actual account, the final payment would usually be adjusted to the remaining amount due, so the simplified total can overstate what is paid. Daily interest calculations, posting dates, and fees can also cause differences.

Assumptions

• The APR and payment amount stay fixed throughout this one-debt estimate.
• Payments are made at the end of each monthly period.
• Interest compounds monthly at APR ÷ 12.
• Fees, taxes, insurance, and other account charges are not included.

How to Build a Snowball Schedule

A full snowball schedule covers multiple debts. List them from smallest balance to largest, while continuing the required minimum payment on every account. Put the remaining amount in the budget toward the smallest balance. When that debt is paid off, roll the payment that was going to it into the next-smallest debt, along with the next debt’s minimum.

For example, imagine three balances of $600, $1,400, and $3,000. If the monthly debt budget allows $500 in total payments, first allocate the required minimums across all three debts and send the remainder to the $600 balance. Once that balance is cleared, keep the same overall budget: redirect its former payment to the $1,400 debt. Repeat for the $3,000 balance. The exact schedule requires each account’s APR, minimum-payment calculation, billing timing, and any relevant fees; this calculator estimates only one balance using a fixed payment.

• Record each balance, APR, minimum due, and due date.
• Sort balances from lowest to highest; do not sort by interest rate for the snowball method.
• Set a consistent total monthly debt budget and reserve the minimum payment for every debt.
• Apply the leftover amount to the smallest balance, then roll its payment forward after payoff.
• Update balances from statements regularly and recalculate when rates or required payments change.

Snowball Versus Avalanche

The snowball method orders debts by balance, smallest first. The debt avalanche method instead directs extra payments to the highest interest rate first while paying required minimums on other debts. If rates, fees, and payments were otherwise modeled consistently, prioritizing the highest-rate balance generally reduces interest compared with prioritizing a smaller, lower-rate balance. The snowball order can clear an individual account sooner when it is small, but the total cost and timeline depend on the actual balances, APRs, and payment rules.

Neither ordering changes the need to keep every account current. A schedule is an arithmetic model, not a change to a creditor’s payment obligations. Use actual statements for amounts due and account-specific terms.

Common Limits and Errors

• Counting the debt budget as extra: The extra amount is in addition to the listed minimum. If the total budget is $250 and the minimum is $50, enter $200 as extra.
• Ignoring other minimums: In a multi-debt plan, minimums on the other accounts still need to be covered; the example’s $250 is the payment on this one debt, not necessarily the whole monthly debt budget.
• Assuming minimums never change: Many accounts calculate required payments using rules that can depend on the balance. A fixed minimum is only a simplifying assumption here.
• Confusing APR with monthly rate: Enter annual APR as a percentage, such as 18, not 0.015. The formula converts it to a monthly decimal.
• Forgetting timing and charges: Interest may accrue daily, payments may post on different dates, and charges can add to the balance. Those details are not represented.

If the monthly payment does not exceed the first month’s modeled interest, the debt will not amortize under this formula and the logarithm cannot produce a valid payoff estimate. The calculator’s formula is intended for a payment that covers interest and reduces principal. For a full multi-account schedule, calculate each month’s interest and minimum due from the actual account terms, then apply the snowball payment order.

Frequently Asked Questions

What is a snowball payment schedule?
A plan that pays minimums on all debts and directs extra funds to the smallest balance first, then rolls that payment into the next-smallest debt after payoff.

Does the calculator show my entire debt-free date?
No. It estimates one balance with a fixed monthly payment. A complete estimate needs every debt’s balance, rate, minimum-payment rule, and the total budget.

Should I enter my total monthly debt budget as extra?
No. Enter the amount left after the minimum payment for this debt. In a multi-debt plan, first account for minimums on all debts.

Why can my statement differ from the estimate?
The estimate uses monthly compounding, fixed payments, and no fees. Actual interest accrual, payment dates, changing minimums, and a smaller final payment can change the result.

Does snowball always cost less interest?
No. The order is based on balance size, not interest rate. Paying the highest-rate debt first may reduce modeled interest when other assumptions are equal, but the actual outcome depends on account terms and payments.

This result is an estimate for educational purposes, and the lender’s disclosure gives the exact figures.

Related

• Debt Snowball Payment Schedule Excel: Build a Payoff Plan
• Debt Snowball Calculator: Google Sheets and Docs
• Debt Snowball Payment Schedule Calculator

in bal | Smallest debt balance | $ | 1000 | 0.01 | 100000000
in apr | Interest rate (APR) | % | 18 | 0.01 | 100
in minp | Monthly minimum payment | $ | 50 | 0.01 | 1000000
in extra | Extra monthly amount | $ | 200 | 0 | 1000000
out months | Estimated payoff months | months | ceil(round(-ln(1 - (apr / 1200) * bal / (minp + extra)) / ln(1 + apr / 1200), 6)) | 0
out total | Estimated amount paid | $ | (minp + extra) * months | 2
out interest | Estimated interest | $ | total - bal | 2