Debt payoff calculator

Each month, interest is added to the balance at a twelfth of the annual rate, then your payment comes off. Whatever is left carries into the next month and is charged interest again. The calculator repeats that until the balance hits zero, counting the months and adding up the interest along the way.

The catch is the first step. If the interest added each month is larger than your payment, the balance never falls. The tool checks that first and tells you the monthly interest your payment has to clear before any of it reaches the balance. Paying even a little above that line is what turns a debt that drifts into one that ends.

The clearing date is the headline, but the number that changes what you do is the monthly interest your payment has to beat. Everything below that line is standing still. A payment sitting a few pounds above it technically clears the balance, and takes years doing it. Nudge the payment up in the calculator and watch how far the date moves for each £25: near the interest line the answer is dramatic, and much further up it flattens off. That curve is what tells you whether finding a bit more each month is worth the effort, or whether you have already taken the win.

The second decision is the rate rather than the payment. A 0% balance transfer changes what the debt costs without changing what you owe, so run the calculator twice: once at 0% for the length of the offer, and once at the rate the card reverts to afterwards, using the balance that would still be outstanding when the offer ends. If the plan clears the balance inside the offer, the transfer fee is the whole cost. If it does not, the leftover balance at the reverted rate is the part worth planning for now rather than later.

If you have more than one balance, this calculator answers one at a time and the real decision is the order. Paying the highest rate first costs the least interest overall. Paying the smallest balance first clears an account soonest, which some people find much easier to keep going with. Both orders finish the job. Which one suits you is a question about you rather than about the arithmetic, and it is worth knowing that the gap between the two is usually smaller than the gap between finding an extra £50 a month and not finding it.

Run each balance through the calculator separately, note the total interest on each, and you have the raw material for that choice. It also shows you something a single balance hides: which debt is quietly costing the most, which is rarely the one with the largest number on it.

Which leaves the question the calculator cannot answer, and it is the one that decides everything above: where the extra payment comes from, month after month, without you ending up back on the card in February. That is a cashflow question about the whole household, not a debt question. Lay every income and every committed payment against the same months, find the surplus that is genuinely repeatable, and point it at the debt. CrestCast does that as a rule for spare cash each month, with a debt payoff planner that orders your cards by rate and then forecasts what a year or five of that actually does to the balances.