How a fixed-repayment loan works
A fixed-repayment loan is any borrowing where you agree an amount, an APR and a length upfront, then pay back the same amount every month until nothing is left to pay, on the schedule fixed when you took it out. Personal loans, car finance and most debt consolidation loans all work this way. Buying a home instead? The Mortgage Calculator handles price, deposit and years.
Every payment does two jobs at once: it covers the interest on whatever is still owed, then reduces what you actually borrowed by whatever is left over. The balance falls a little each month, so the interest charged on it falls too, so what the level payment buys shifts gradually from mostly interest towards mostly principal. One formula produces that fixed payment:
The calculator's own numbers make this concrete: 10,000 borrowed at 7% APR over 36 months puts r at roughly 0.5833% a month and n at 36, and the formula returns a monthly payment of 308.77. Over the full 36 months that adds up to 11,115.75 handed back, 1,115.75 of it interest on top of the 10,000 borrowed.
APR is not the rate on the advert
The percentage printed on a loan advert is not always the number that formula should use. Lenders can headline a lower flat rate that ignores fees, and some products carry a mandatory arrangement fee buried in the credit agreement. APR, or APRC for anything secured against a property, folds every mandatory cost into one annual percentage spread evenly across the term, which is why it appears on every UK credit advert and quote by law. It is the only figure worth comparing between two lenders: put the APR from each offer into this calculator with the same amount and the same term, and the lower total repayable is genuinely the cheaper loan, fees included. Never weigh a flat rate from one lender against an APR from another; they are not measuring the same thing, and the gap can be wide enough to flip which offer wins.
The term trade-off
Stretching the term lowers the monthly payment and raises the total interest, because a longer term leaves more months for interest to build on a slower-falling balance. Shortening the term does the reverse. Neither direction is automatically right; it depends on what the monthly budget can absorb against how much the total cost may grow.
Using the same 10,000 at 7% APR, moving from a 36-month term to a 60-month term drops the monthly payment from 308.77 to 198.01, a genuine difference if the budget is tight. It also lifts the total interest from 1,115.75 to 1,880.72, an extra 764.97 for the lower payment. The "Same loan, different terms" table above runs this comparison automatically across seven common term lengths, so the trade-off is visible before a term gets picked rather than after.
How to actually compare two offers
A fair comparison holds the amount and the term fixed and lets only the APR move; change any of the three and the comparison stops meaning anything. A monthly payment that looks only a little higher can still belong to the worse deal once the term runs its course: on 10,000 over 36 months, moving from 7% to 9% APR adds only about 9.23 to the monthly payment, yet it adds 332.15 to the total repaid, because that small monthly gap gets charged for three years straight. The "Rate check" table above holds the amount and term fixed and moves only the APR, precisely so two offers can be lined up like this without working the sums by hand. Ask every lender for the APR rather than the rate, and ask what fees sit inside it: some are folded in, some are charged separately, and the second kind will not appear here until added to the amount borrowed.
Paying a loan off early
Most credit agreements allow some form of early or partial repayment, and in the UK the Consumer Credit Act gives borrowers a statutory right to settle a regulated agreement early, with the lender required to reduce the interest charged to reflect the time saved. Many personal loan and car finance providers go further, allowing ad-hoc overpayments or a full early settlement at any point, sometimes with a small settlement calculation involved. The detail differs by lender and by product, so the credit agreement, or a quick call to the lender, is the only reliable source for what a specific loan allows and what it costs to act early. Whatever the mechanics, clearing a loan faster than scheduled always cuts the interest charged on the balance that disappears early, for the same reason a shorter term does.
Questions people ask
What monthly payment can I afford?
A common rule of thumb keeps all debt repayments, this loan included, under roughly 20% of take-home pay, with housing costs and debt together under about 36%. Treat that as a rough ceiling, not a guarantee, since the rest of the budget matters too. A dedicated tool using income and existing debts rather than a flat percentage is on the build list; the Debt-to-Income Ratio Calculator holds that spot for now.
Does checking loan rates hurt my credit score?
Usually not, if the lender or comparison site describes the check as a "soft search", a "quote" or an "eligibility check", standard before a real application and invisible to other lenders. A "hard search", run once an application actually goes in, does appear on a credit file and can affect a score slightly, more so if several happen in a short space of time. Look for the words "soft search" or "no impact on your credit score" before comparing several lenders.
Fixed or variable rate, which is better for a personal loan?
Most personal loans and car finance deals are fixed already: the APR and the monthly payment lock in at the start and do not move for the life of the agreement, which is exactly what this calculator assumes. Variable-rate personal borrowing exists but is far less common than variable-rate mortgages, and it carries the same trade-off: payments can move with the reference rate, up or down, which makes budgeting harder. Fixed is the steadier default unless a specific product gives a clear reason to prefer variable.
Why is my quoted rate different from the one in the advert?
UK advertising rules only require a lender to give its advertised "representative APR" to at least 51% of people who go on to be accepted, not to everyone who applies. Your own credit history, income, and the size and term of the loan all feed into your personal rate, which can land higher or lower than the advert. Being accepted is not the same as getting the advertised rate; use the figure on your actual offer in this calculator, not the number from the advert.
Should I pay off a loan early?
Usually yes on interest grounds alone, since clearing a balance early always stops interest building on the part that is gone. Check first for an early settlement fee that could outweigh the interest saved, and whether the money would do more good clearing a higher-rate debt such as a credit card, or sitting in an emergency fund, since this loan is probably already the cheapest debt in the household.
These figures are estimates for a simple fixed-rate, fixed-term loan, not financial or lending advice. What a lender actually offers depends on fees, your credit file and its own underwriting, so check the credit agreement, or ask the lender directly, before signing anything.