Credit Card Payoff Calculator: Minimum vs. Fixed Payment

Disclaimer: This calculator is provided for educational and estimation purposes only and does not constitute formal financial advice.

The question behind the calculator

“How long will it take to pay off my credit card” is the single most common question in personal finance, and it almost always has a second half attached: “and what happens if I just paid more.” This tool answers both at once, for one balance. Enter what the statement actually says — balance, APR, and the minimum-payment formula the issuer uses — then enter a fixed amount you could realistically pay every month instead. The calculator runs both plans forward until each one reaches zero and reports the months and total interest for each, plus the headline numbers: how much sooner, and how much cheaper, the fixed plan is. If the real question is which of several cards or loans to attack first with limited extra money, that is a different calculation — see the debt snowball vs. avalanche calculator instead. This tool deliberately stays narrow: one balance, one what-if.

How the minimum payment actually works

Card issuers do not bill a flat minimum. Almost every major agreement bills the greater of a small flat floor or a percentage of the balance plus that statement’s interest:

Here $B_t$ is the balance entering month $t$, $F$ is the flat dollar floor, and $p$ is the percentage rate — 2% and $35 by default here, both adjustable, since issuers vary. The mechanism that makes minimum-only payoffs drag on for years is built into this formula: as $B_t$ falls, the percentage portion of $M_t$ falls with it, so the required payment keeps shrinking right alongside the balance. Only once the percentage portion drops below the flat floor does the payment stop shrinking — from that point it is effectively a fixed payment, and the last stretch behaves like the fixed plan below.

How the fixed-payment plan works

The second plan is simpler: pick one dollar amount, $P$, and pay exactly that every month regardless of how the balance moves. Both plans share the same underlying balance update —

— with $\text{payment}_t$ equal to $M_t$ for the minimum plan and to the constant $P$ for the fixed plan. The $\min(\cdot)$ term matters at the very end of either payoff: it stops the last month’s payment from overshooting a balance smaller than what’s owed. Total interest paid is the running sum of every $I_t$ until the balance reaches zero, or until 30 years pass without that happening — the same search ceiling used elsewhere on this site so a payment that never outpaces its own interest is reported as unreachable rather than simulated forever.

A worked example: $5,000 at 22.99% APR

The calculator’s defaults are a realistic mid-sized card balance. At a 2%

• interest minimum with a $35 floor, that balance’s very first required minimum payment is $196, of which $96 is interest already claimed before a single dollar touches principal. Paying the minimum only, from here, takes 10 yr 1 mo and costs $4,279 in interest — more than 85% of the original balance. Paying $200 a month instead — barely $4 above that first minimum — clears the same balance in 2 yr 11 mo for $1,871 in interest, a savings of $2,408 and 86 fewer months of payments.

Every row here is measured against the same 10 yr 1 mo, $4,279-interest minimum-only baseline. The relationship is not linear — doubling the payment from $150 to $300 does not simply double the savings — because a bigger payment shortens the window interest has to compound, and that window shrinks faster than the payment grows.

Why “sooner” and “cheaper” can disagree

The $125 row above is worth pausing on, because it looks like a mistake and is not one. It finishes 44 months sooner than the minimum-only plan, yet costs $298 more in interest. The reason is the minimum formula’s own shape: its first required payment on this balance is $196 — comfortably above $125 — and it only declines from there as the balance falls. For a long stretch early in the payoff, the minimum-only plan is quietly paying down principal faster than a flat $125 would, because the percentage-of-balance formula has not caught up to $125 yet. A $125 fixed payment carries a larger balance than the minimum-only plan would at the same point, for longer, which is exactly what interest is charged on. It still finishes first, because it never slows down the way the declining minimum eventually does — but the early months cost more than they saved later. This is exactly why both numbers are reported separately instead of collapsed into one “better/worse” verdict: a fixed payment only beats the minimum plan outright once it clears that formula’s starting requirement by a comfortable margin, not the moment it exceeds today’s minimum in isolation.

When a payment cannot get you to zero

Enter a fixed payment that does not exceed the interest a balance is currently accruing, and the balance holds steady or grows — there is no number of months that gets it to zero. A $10,000 balance at 24% APR accrues $200 in interest every month; a $150 fixed payment there never reduces the balance at all, since it does not even cover the interest, let alone touch principal. Rather than let a simulation run forever chasing a balance that never shrinks, or divide by a gap that could be zero, the calculator checks the same 30-year ceiling used for the minimum-only plan and reports the fixed plan as unreachable the instant that ceiling passes without a zero balance. The fix is always the same: raise the payment until it clears the interest shown in the note beneath the results by a real margin, not by a few dollars.

Reading your own numbers

Pull the balance and APR straight from the most recent statement — not a round number. The minimum-payment percentage and flat floor are on the same statement, usually in the small type near the minimum-payment line or in the cardholder agreement; 1%–3% and a $25–$35 floor cover the large majority of major US issuers, and both defaults here are adjustable if a specific card states something else. The “your monthly payment” field is the one number actually worth experimenting with: try the highest amount realistically sustainable every month, not just this month, since a fixed plan abandoned after three months saves nothing the note above promises. The interest-saved and months-saved figures update on every keystroke, so it costs nothing to test several amounts before committing to one.

If a student loan is competing for the same extra dollars, run it through the student loan payoff calculator too — comparing both cards’ worth of interest saved per dollar of extra payment is how you decide which balance actually deserves the money first.