How credit card payoff time is calculated

What the payoff estimate answers

Given a balance, APR, and a fixed monthly payment you plan to hold constant, how many months might it take to reach a near-zero balance, and how much interest might accrue along the way?

That is a simulation under assumptions — not credit counseling, and not an issuer’s minimum-payment formula.

Try the credit card payoff calculator. For several debts and payment orderings, use the debt payoff calculator and the guide on snowball vs avalanche.

Month-by-month mechanics

monthlyRate = APR ÷ 100 ÷ 12

Each month:

1. interest = balance × monthlyRate
2. Apply the payment after interest
3. Principal reduction = payment − interest (when positive)
4. Update the remaining balance

The final payment is capped to remaining balance plus that month’s interest, so the last payment is often smaller than your regular payment.

The simulation stops when the balance is within a small tolerance (half a cent in this site’s MVP) or hits a safety cap (1,200 months).

Outputs you typically see

• Months to payoff
• Total payments and total interest
• Final payment amount
• A month-by-month schedule

Zero balance with a valid setup yields immediate payoff (0 months, 0 interest) without treating that as an error.

Assumptions

• Fixed monthly payment every month until payoff
• No new charges, annual fees, or penalty APRs
• Monthly periodic rate = APR/100/12
• Final payment capped to remaining balance + interest

Limitations

• Does not model issuer minimum-payment formulas or promotional APRs unless you enter equivalent numbers yourself
• Does not invent late fees or penalty pricing
• Daily interest conventions at an issuer may differ from this monthly model

Takeaways

Payoff time is the length of a fixed-payment simulation at your APR — useful for comparing payment amounts under identical assumptions, not for predicting an issuer’s exact statement math.