What this calculator works out
This calculator takes a card balance, its APR and the fixed monthly payment you intend to make, and works out how many months the balance will take to clear, how much interest you will pay along the way and what the debt will cost in total.
It works by simulating the balance month by month rather than using a single formula: it adds that month's interest, subtracts your payment, and repeats until the balance reaches zero. That is exactly how a card actually behaves, so the answer is reliable provided you keep making the payment and stop adding new spending.
Enter your details
Before you enter your figures
- Use the purchase APR from your statement, not the rate advertised for new customers. Cash advances and balance transfers are often charged at different rates.
- Check whether a promotional 0% period is still running and when it ends. This calculator applies one rate for the whole period, so run it separately for the promotional period and for what follows.
- Enter the payment you will genuinely make every month, including the months containing Christmas and the car insurance renewal.
- Assume no further spending on the card. Adding new purchases while repaying resets the arithmetic entirely.
A minimum payment is typically calculated as a small percentage of the balance plus that month's interest. Because it falls as the balance falls, it stretches repayment over a very long period. Paying the minimum is not a neutral choice — it is the most expensive way to clear a card.
How this calculator works
The calculator repeats three steps each month until the balance is cleared:
Monthly rate = APR ÷ 12 ÷ 100
Interest this month = balance × monthly rate
New balance = balance + interest − paymentIf your payment does not cover the first month's interest, the balance would grow indefinitely, so the calculator stops and tells you the payment is too low rather than returning a meaningless number.
Dividing the APR by twelve gives a nominal monthly rate. Card issuers compound daily and apply the rate to the statement balance, so a real statement may differ by a small amount. The difference is immaterial for planning and does not change any decision.
Worked example: £3,000 at 24.9% APR
Using the default figures — a £3,000 balance at 24.9% APR, paying £150 a month:
- Monthly rate: 24.9% ÷ 12 = 2.075%
- First month's interest: £3,000 × 2.075% = £62.25, so only £87.75 of the £150 reduces the balance
- Time to clear: 27 months
- Interest paid: £915.95
- Total paid: £3,915.95
Now compare that with paying the minimum. On a typical minimum of 1% of the balance plus interest, the same £3,000 takes roughly 28.8 years to clear and costs close to £6,000 in interest — twice the original balance. The £150 payment is not marginally better than the minimum; it is a different outcome entirely. This gap is the single most useful thing this calculator shows.
Common mistakes
- Continuing to spend on the card. New purchases extend the term and, on many cards, are paid off after the higher-rate balances.
- Assuming the promotional rate lasts. When a 0% period ends, the full purchase APR applies to whatever remains.
- Paying the minimum because it is the amount shown. The minimum is the lender's floor, not a recommendation.
- Overlooking balance transfer fees. A transfer typically costs 2–4% of the balance up front, which must be weighed against the interest saved.
- Clearing the lowest-rate card first while a higher-rate one keeps growing.
Frequently asked questions
Should I pay this card or save the money instead?
In almost every case, clear the card. A card at 24.9% costs far more than any savings account currently pays, so repaying it is the best guaranteed return available to you. The one sensible exception is holding a small emergency buffer first, so that an unexpected cost does not go straight back onto the card and undo the progress.
Is a balance transfer worth it?
Often, if you are disciplined about it. Compare the transfer fee against the interest you would otherwise pay — on the example above, a 3% fee is £90 against £916 of interest, which is clearly worthwhile. The risks are that you treat the freed-up credit as spending capacity, or that you reach the end of the promotional period with a balance remaining and no new offer available.
What is the difference between APR and interest rate?
APR is designed to be a comparable annual figure that includes certain compulsory charges as well as interest, which is why it is the number to compare between products. For a straightforward credit card with no annual fee the two are usually close. Always compare APR with APR rather than mixing the two.
Why does my statement show slightly different interest?
Card issuers usually calculate interest daily on the balance outstanding and apply it monthly, and many charge no interest on new purchases if the statement balance is cleared in full. This calculator uses a simpler monthly model. Expect small differences of a few pounds over a repayment period, not large ones.
What if I cannot afford a payment that clears the balance?
Speak to someone before it escalates. Free, confidential debt advice is available in the UK from Citizens Advice, StepChange and National Debtline. Lenders are also required to treat customers in financial difficulty fairly, and may be able to freeze interest or agree a reduced payment plan. Doing this early keeps far more options open than waiting.
Related tools
References
- MoneyHelper — free guidance on credit cards, balance transfers and dealing with problem debt
- Financial Conduct Authority — rules on credit card disclosure, persistent debt and treatment of customers in difficulty
Sources are checked at publication and can change — how I choose and check references.