Two ways of asking "how long"
A card balance, an APR and a payment are enough to work out how long a payoff takes, but "a payment" means different things depending on how it is set. A fixed payment stays level until the balance clears, so more of each payment goes toward principal as the balance falls, and the payoff accelerates. A minimum payment usually does the opposite: recalculated from the balance itself, it falls as the balance does, dragging the payoff out. This calculator simulates both, and puts a shrinking minimum directly against a fixed payment of the same starting amount so the difference is visible. A second tab flips the question round: given a target number of months, what fixed payment gets there.
Paying a fixed amount
A fixed payment on a card balance behaves exactly like a fixed-repayment loan: every payment covers that month's interest first, and whatever is left over reduces the balance, so each month's interest shrinks a little and a level payment buys slightly more principal than the one before. There is no simple total for how long that takes without a bit of algebra, but the standard amortising-payment formula rearranges cleanly for the number of payments once the payment itself is fixed:
A 3,000 balance at 21.9% APR, paid down at a fixed 150 a month, clears in 26 months (2 years 2 months) and costs 766.67 in interest, 3,766.67 repaid in total. Raise the payment and both figures fall together, since less time carrying a balance means less interest charged on it.
How a minimum payment actually behaves
Card minimums are not one universal number. Issuers commonly set them as the greater of a percentage of the outstanding balance or a fixed floor, most often around 1 to 2.5% of the balance or a floor of 5 to 25, whichever is higher, though the exact percentage, floor and whether fees are folded in vary by issuer and by card, so treat any single figure as representative rather than universal. This calculator uses a typed percentage (2.5% by default) or a typed floor (25 by default), whichever is higher, recalculated fresh every month against whatever the balance has fallen to.
That rule produces two phases. Early on, while the balance is large, the percentage almost always exceeds the floor, so the payment shrinks in step with the balance, a slowly declining tail. Once the balance falls far enough that the percentage would dip below the floor, the floor takes over and holds the payment flat for the rest of the schedule. On the 3,000 balance at 21.9% APR from the previous example, with a 2.5% minimum and a 25 floor, that crossover happens once the balance reaches 1,000 (25 ÷ 2.5%), which this simulation reaches at month 164. The whole schedule takes 235 months, 19 years 7 months, and costs 6,217.35 in interest, roughly eight times the interest on the same balance paid down at a level 150 a month.
Why fixing the payment changes so much
The comparison this calculator draws out in minimum mode is worth lingering on: take that first minimum payment, the largest one in the whole shrinking schedule, and simply hold it fixed instead of letting it fall. Here, that first payment is 75 (2.5% of 3,000). Paid at a level 75 a month, the same balance clears in 73 months, 6 years 1 month, for 2,429.94 in interest, against 235 months and 6,217.35 on the declining schedule, a saving of 13 years 6 months and 3,787.41. Nothing about the starting payment changes, only whether it is allowed to fall. Money Saving Expert's account of the FCA's persistent-debt rules cites a near-identical case at a different rate: a 3,000 balance at 17.9% APR taking 27 years on minimums alone, cut to about 5 years by fixing the payment at its starting level. The chart above plots both paths on your own numbers so the gap is something you can see, not take on trust.
Choosing a target date instead
The second tab runs the same formula the other way: given the balance, the APR and a target number of months, what fixed payment clears it exactly on time, the standard amortising-payment formula, closed form:
The same 3,000 balance at 21.9% APR, targeted at 24 months, needs a fixed payment of about 155.49 a month, 731.67 in interest over the full term. Like most planning tools, this compounds monthly for simplicity; a card issuer actually charges interest daily on the average balance carried each day of the billing cycle, so a real statement will differ slightly, more so on a balance that swings a lot within a month. For a steady balance the monthly approximation is close enough to plan against.
How card interest actually accrues
A card's APR is an annual figure, but the interest is worked out daily. Issuers divide the APR by 365 to get a daily periodic rate, then apply it to the average balance carried each day of the billing cycle, added up and charged at the end of it. That is why paying down part of a balance partway through a cycle still saves some interest for the rest of that cycle, rather than waiting for the next statement. Purchases behave differently: if a statement is paid in full by its due date, new purchases on it usually carry a grace period, typically three to three and a half weeks, with no interest at all. The moment any balance is carried past its due date, that grace period is gone for both the carried balance and any new purchases, which accrue interest from the day they post.
Why minimum payments are shaped the way they are
A minimum payment exists to keep an account in good standing, not to clear it in any particular time, so issuers set it low enough that most cardholders can meet it even when money is tight. A percentage-of-balance structure scales that requirement to what is actually owed rather than a flat amount regardless of balance size, and the floor exists so a small balance still generates a payment worth processing. Regulators take a direct interest in what that produces over years rather than months: the UK's Financial Conduct Authority requires issuers to write to customers stuck in "persistent debt", paying more in interest and fees over 18 months than they repay of the balance, with escalating prompts at 18, 27 and 36 months, and treats a "reasonable period" to clear a balance as three to four years rather than the far longer spans a bare minimum can stretch to. None of that makes the minimum a trap by design so much as a floor that was never meant to be the only number anyone pays.
A word on 0% balance transfers
Moving a balance to a card offering a 0% promotional rate is a genuinely different way to cut this interest, rather than a variation on the fixed-versus-minimum question above. It is not a free move: transfers typically carry an upfront fee as a percentage of the amount moved, and the 0% rate applies only until the promotional period ends, after which the remaining balance reverts to a standard rate that can be as high as the one being escaped. Whether a transfer beats paying this balance down in place depends on the fee, the 0% window against how many months a fixed payment here would take, and realistic confidence the balance clears before the promotional rate expires, figures specific to the offer rather than something a general calculator can price in.
Questions people ask
Why does this calculator simulate the minimum payment instead of using one formula?
Because a minimum payment is recalculated from the current balance every month, so it keeps shrinking as the balance falls. There is no single formula for a payment that changes as the balance itself changes, so this calculator works through it month by month instead.
Is 2.5% of the balance and a 25 floor exactly what my card charges?
Probably not exactly. Issuers commonly set minimums somewhere around 1 to 2.5% of the balance or a floor in the 5 to 25 range, whichever is higher, but the precise figures vary by issuer and by card. Both are editable above; check your card's terms or a recent statement to match your account precisely.
What does the "floor kick-in" point in the results mean?
Early in a minimum-payment schedule the percentage almost always produces a bigger number than the floor, so the payment shrinks with the balance. Once the balance falls far enough that the percentage would dip below the floor, the floor takes over and holds the payment flat for the rest of the schedule. The results note the exact month that switch happens.
What does it mean if my payment or minimum never clears the balance?
A fixed payment at or below the interest that balance generates in its first month can never reduce it, since nothing is left over once that interest is covered. A minimum's percentage has the same problem if it sits at or below the monthly interest rate. Either case is flagged directly, with the exact figure the payment needs to clear.
Why does fixing the payment at the starting minimum save so much?
A shrinking minimum spends less time attacking the balance the longer it runs, since the payment keeps falling alongside it. Holding that same starting amount fixed keeps the pressure constant, so the acceleration a level payment normally produces actually happens instead of being cancelled out by a payment that is shrinking at the same time.
Why does this calculator assume monthly compounding when cards charge interest daily?
Monthly compounding is the standard simplification most planning tools use, since it only needs a monthly APR, term and balance rather than a full daily transaction history. It tracks a real statement closely for a steady balance, less closely for one that swings a lot within a billing cycle.
Should I use a 0% balance transfer instead of paying this off in place?
Possibly, if the transfer fee is small relative to the interest saved and the balance can realistically clear, or be moved again, before the 0% period ends. It depends on the specific fee and promotional length on offer rather than anything a general calculator can price in.
These figures are estimates assuming monthly compounding and payments made on time and in full; real statements accrue interest daily on the average balance and vary by issuer. This is a planning tool, not financial advice, so check your own card's terms before relying on any figure here.