Credit Card Payoff with Fixed Payment Calculator

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Table of contents

• How to use
• Common mistakes
• Definitions
• Methodology
• Limitations & assumptions
• Sources

Current balance ($): The credit card balance you want to pay off before adding any future purchases.

APR (percent): Annual percentage rate, the yearly interest rate shown on a credit card account or statement.

Monthly rate: The APR divided by 12 months, used here to estimate one month of interest.

Fixed monthly payment ($): The same planned payment amount used each month until the final payment, which may be smaller.

First-month interest: The estimated interest added during the first month before your payment is applied.

First-month balance drop: The part of the first payment that lowers the balance after first-month interest is covered.

First payment used by interest: The percent of the first payment that goes to interest instead of lowering the balance.

Payment to finish in 36 months: A fixed-payment benchmark that estimates the monthly payment needed to pay the balance in 36 monthly payments.

Mistake: Entering Current balance ($) with planned future purchases included.
Fix: Use only the balance you owe now, and recalculate later if new charges are added.

Mistake: Leaving APR (percent) blank or entering a monthly rate instead of the annual rate.
Fix: Enter the yearly APR from your statement, such as 19.99, and use 0 only for a true 0 percent rate.

Mistake: Using Fixed monthly payment ($) for a changing minimum payment.
Fix: Enter the steady amount you plan to pay every month; this calculator does not model a minimum payment that falls as the balance falls.

Mistake: Ignoring Payment check when the payment is too low to reduce the balance.
Fix: Increase Fixed monthly payment ($) until it is higher than First-month interest.

Mistake: Treating Estimated payoff month as an exact card due date.
Fix: Use it as a month-level estimate based on First payment date, then check your card statement for the real due date.

Mistake: Expecting Total paid to equal Fixed monthly payment ($) times Time to pay off.
Fix: Check Final payment; the last payment can be smaller than the regular monthly payment.

• The interest model uses a simple monthly rate equal to APR divided by 12. Real cards may use daily interest, different billing-cycle lengths, grace-period rules, and issuer rounding.
• The payoff estimate assumes no new purchases, cash advances, balance transfers, annual fees, late fees, or APR changes.
• Fixed monthly payment ($) is treated as the same amount every month until the last payment. The calculator does not model a changing minimum payment.
• Estimated payoff month is based on monthly steps from First payment date. It is not a statement due-date or billing-cycle calculator.
• If the payment does not cover the first month's interest, the calculator does not show a payoff time because the balance would not shrink under this fixed-payment plan.
• The loop has a long-horizon safety cap. Very long payoff plans may be reported as too long to estimate reliably with this simple monthly model.
• Payment to finish in 36 months is a planning benchmark, not a promise that your issuer will accept that amount as a required payment.

Monthly interest rate

The calculator converts APR (percent) to a monthly rate by dividing by 100 and then by 12.

monthly_rate = apr_percent / 100 / 12

Payoff loop

Each month, the calculator adds interest to the starting balance, applies the fixed payment, and counts one payment. In the final month, payment_used is limited to the amount due, so the final payment can be smaller than Fixed monthly payment ($).

interest = balance_start * monthly_rate

amount_due = balance_start + interest

payment_used = min(monthly_payment, amount_due)

balance_end = amount_due - payment_used

Total interest paid is the sum of all monthly interest amounts. Total paid is the original balance plus Total interest paid.

total_paid = starting_balance + total_interest

Payment check

If APR is greater than 0 and the fixed payment is less than or equal to the first month's interest, the plan is not feasible because the balance does not go down.

if monthly_rate > 0 and monthly_payment <= starting_balance * monthly_rate, payoff is not feasible

First payment details

First-month interest is the starting balance times the monthly rate. First-month balance drop is the payment minus that interest, unless the card is paid off in the first month.

first_month_interest = starting_balance * monthly_rate

interest_share_first_payment = first_month_interest / monthly_payment * 100

36-month payment benchmark

For a 0 percent APR, the 36-month payment is the balance divided by 36. Otherwise, the calculator uses the standard fixed-payment amortization formula.

if monthly_rate = 0, payment_36_months = balance / 36

if monthly_rate > 0, payment_36_months = balance * monthly_rate / (1 - (1 + monthly_rate)^(-36))

Small payment increase check

The If you paid a little more table reruns the same payoff loop with Fixed monthly payment ($) plus $25 and plus $50. Months saved equals the base payoff months minus the test payoff months. Interest saved equals the base Total interest paid minus the test interest.

months_saved = base_months - test_months

interest_saved = base_interest - test_interest

Mini-example

For Current balance ($) of $1,000, APR (percent) of 12, and Fixed monthly payment ($) of $100, the monthly rate is 1 percent. First-month interest is $10, so the first payment lowers the balance by $90. The payoff takes 11 months, Total interest paid is about $58.98, Total paid is about $1,058.98, and Final payment is about $58.98. Paying $25 more saves about 2 months and $11.37 of interest; paying $50 more saves about 4 months and $18.88 of interest.