Debt & Borrowing

How Loan Interest Really Works in the UK — Amortisation, APR & the True Cost of Borrowing

Q: Why does so much of my early loan payment go to interest?

This is amortisation — your monthly payment is fixed, but how it splits between interest and principal changes every month. In month one, interest is charged on the full loan balance, so it takes a big slice. As you pay down the balance, the interest portion shrinks and the principal portion grows. By the final months, nearly your whole payment is clearing principal. This is normal and mathematically unavoidable on a standard repayment loan.

Q: What does APR actually mean on a loan?

APR stands for Annual Percentage Rate. It represents the annual cost of borrowing as a percentage — including the interest rate and any mandatory fees. By law, UK lenders must quote APR so you can compare loans on a like-for-like basis. The 'representative APR' is the rate at least 51% of accepted applicants receive — your personal rate may be higher based on your credit profile. Always compare the total amount repayable, not just the monthly payment or the APR in isolation.

Q: How much does extending a loan term cost in extra interest?

Extending the term reduces your monthly payment but significantly increases total interest. On a £10,000 loan at 7.9% APR: a 3-year term costs £1,228 in interest; a 5-year term costs £2,059 — an extra £831 to reduce monthly payments by £133. The longer the term, the more the lender makes. Only extend if your budget genuinely requires lower monthly payments.

Q: Can I overpay a personal loan without penalty?

Under the Consumer Credit Act, you have the right to overpay or settle a personal loan early at any time. Lenders can charge an early repayment charge (ERC) of up to 58 days' interest on the amount being repaid early. This cap means overpayments are almost always worthwhile — the interest you save will typically far exceed any ERC. Check your loan agreement to confirm your specific terms.

Q: What is the difference between a personal loan and a credit card for borrowing?

Personal loans have fixed monthly payments, a fixed end date and usually a lower APR for amounts over £3,000. Credit cards have flexible payments (minimum or more), no fixed end date and typically higher APRs — though 0% deals can make them very cheap for short-term borrowing. For amounts over £3,000 you want to repay over more than 12 months, a personal loan is usually cheaper. For smaller amounts or short repayment periods, a 0% credit card beats most personal loan rates.

Updated May 2026 · UK personal loans 2026/27 · 9 min read

What is amortisation and why it matters

When you take out a UK personal loan, the lender calculates a fixed monthly payment that will clear the full balance — principal plus all interest — by the end of the agreed term. This process is called amortisation.

The word comes from the French "amortir" — to kill or extinguish. Every payment you make kills off a small portion of the debt. The twist is that the split between interest and principal changes every single month — even though your payment stays the same.

Understanding amortisation changes how you think about debt. It reveals:

Why paying extra early saves so much more than paying extra later
Why longer loan terms cost dramatically more even if the monthly difference seems small
Why a low monthly payment is not the same as a cheap loan

Why early payments are mostly interest

Each month, interest is calculated on the current outstanding balance. In month one, that balance is the full loan amount — so the interest charge is at its highest. As you pay down the balance month by month, the interest charge falls and an increasing proportion of your fixed payment goes toward principal.

Here's what that looks like in practice for a £10,000 loan at 7.9% APR over 3 years (monthly payment: £313.40):

Month	Opening balance	Interest	Principal	Closing balance
1	£10,000.00	£65.83	£247.57	£9,752.43
2	£9,752.43	£64.20	£249.20	£9,503.23
6	£8,755.18	£57.63	£255.77	£8,499.41
12	£7,312.44	£48.13	£265.27	£7,047.17
24	£4,056.52	£26.70	£286.70	£3,769.82
36	£311.34	£2.05	£311.35	£0.00

In month one, £65.83 goes to interest and £247.57 goes to reducing the debt. By month 36, almost the entire payment clears principal. This is why overpaying in the early months is so powerful — every extra pound reduces the balance on which future interest is calculated.

Use the Loan Repayment Calculator to see your own amortisation

Enter your loan details to see the full year-by-year breakdown of interest vs principal for any loan. Open calculator →

APR explained — what it means and what it misses

APR stands for Annual Percentage Rate. In the UK, lenders are required by the FCA to quote it on all loan products so you can compare on a level playing field.

What APR includes

The interest rate charged on the outstanding balance
Any mandatory fees charged as part of the loan (arrangement fees, etc.)
The timing of payments and how interest compounds

What APR does NOT tell you

Total amount repayable: APR is a rate, not a pound figure. Always ask or calculate the total you'll repay.
Your personal rate: Advertised APR is the "representative" rate — offered to at least 51% of accepted applicants. Your rate may be higher.
Optional fees: Some lenders offer optional Payment Protection Insurance (PPI replacements) that are excluded from the APR calculation.

Representative APR is not a promise

Lenders must give you a personalised rate before you sign. If the rate offered is higher than the representative APR, you are under no obligation to proceed. Use soft-search eligibility checkers before applying — they show you the rate you'll likely receive without leaving a mark on your credit file.

Typical UK personal loan APRs in 2026

Loan amount	Typical APR range	Common lenders
£7,500–£25,000	5.9%–7.9%	Banks, building societies, supermarket lenders
£3,000–£7,500	9%–15%	Banks, online lenders
£1,000–£3,000	15%–30%	Online lenders, credit unions
Credit cards	20%–30%+	Card providers (0% deals for good credit)
Credit unions	Up to 42.6% APR cap	Community lenders — often best for small amounts

How loan term affects total interest

Extending the loan term reduces your monthly payment — but significantly increases the total interest you pay. This is one of the most important and most overlooked aspects of loan cost.

Term	Monthly payment	Total interest	Total repaid
2 years	£452.27	£854.52	£10,854.52
3 years	£313.40	£1,282.40	£11,282.40
4 years	£243.59	£1,692.12	£11,692.12
5 years	£202.49	£2,149.40	£12,149.40
7 years	£154.21	£3,153.24	£13,153.24

£10,000 loan at 7.9% APR. Monthly payments rounded.

Going from a 3-year to a 5-year term saves £110.91/month — but costs an extra £867 in interest. The longer term is only cheaper in one narrow sense: the monthly cash outflow. Over the life of the loan, you pay substantially more.

The right term is the shortest you can comfortably manage

Choose the shortest term your monthly budget can support. If you can manage the 3-year payment, don't take 5 years. The interest saving is real money.

Overpayments — the most powerful lever

Making overpayments on a personal loan reduces the outstanding principal faster, which means less interest accumulates on each subsequent month's calculation. The savings compound over the remaining term.

How overpayments work

Any amount above your contractual monthly payment reduces the outstanding principal directly
From the following month, interest is calculated on a lower balance
Your contractual payment stays the same — but a larger portion goes to principal
The loan clears earlier than the original term

Overpayment impact — £10,000 loan at 7.9% APR over 5 years

Standard monthly payment: £202.49. Total interest: £2,149.40.

Extra payment	Interest saved	Term reduced by	Total paid
£0/month	—	—	£12,149.40
£50/month	£486	12 months	£11,663.40
£100/month	£800	21 months	£11,349.40
£200/month	£1,153	32 months	£10,996.40

Adding just £50/month to a £202.49 payment saves nearly £500 and clears the loan a full year earlier. The extra £600/year spent saves £486 in interest — almost a wash — but you're debt-free 12 months sooner.

Check for early repayment charges (ERCs) first

UK personal loan lenders can charge up to 58 days' interest as an ERC on overpayments. On a £10,000 loan at 7.9%, 58 days' interest is approximately £125 — small relative to the interest you'd save. Read your loan agreement or call your lender to confirm the ERC terms before overpaying significantly.

Three worked examples

Example 1 — Emma: Home improvement loan

Emma borrows £8,000 at 6.9% APR over 3 years to renovate her kitchen.

Monthly payment: £246.65
Month 1 interest: £46.00 | principal: £200.65
Month 36 interest: £1.41 | principal: £245.24
Total interest paid: £879.44
Total repaid: £8,879.44

Emma's loan costs £879 in interest over 3 years — 11% of the amount borrowed. If she pays an extra £100/month, she clears in 25 months and saves £306 in interest.

Example 2 — James: Debt consolidation

James has three debts totalling £15,000 at an average 22% APR. He consolidates into a single loan at 9.9% APR over 5 years.

Old monthly minimum payments: approx. £420 (combined, mostly interest)
New single monthly payment: £317.97
Interest saving vs keeping old debts (estimate): £4,200+ over term
Total interest on new loan: £4,078.09
Total repaid: £19,078.09

Consolidation lowers James's monthly payment by over £100 and could save thousands in interest — but only if he doesn't accumulate new debt on the cleared cards. The consolidation loan's discipline is what makes it work.

Example 3 — Priya: Short-term borrowing decision

Priya needs £2,000 urgently. She compares her options:

Personal loan at 24.9% APR over 2 years: £104.07/month → £498 total interest
0% credit card for 18 months: £111.11/month (to clear in 18 months) → £0 interest if cleared
Arranged overdraft at 39.9% EAR: variable, approximately £65/month interest only

The 0% credit card is cheapest if Priya is confident she'll clear it in 18 months. The personal loan is safer if she needs the certainty of a fixed schedule. The overdraft is the most expensive if she doesn't pay it down actively.

Personal loan vs credit card — which costs less?

Factor	Personal loan	Credit card
Typical APR	6%–25% (amount dependent)	20%–30% (0% deals available)
Fixed repayment end date	Yes — built in	No — you choose minimum or more
Monthly payment flexibility	Fixed (overpayments usually allowed)	Flexible — minimum or more
Best for amounts	£3,000+	Under £3,000 (especially with 0%)
Best for repayment period	Over 12 months	Under 12 months (0% deal)
Risk of extending debt	Low — fixed schedule	High — easy to pay minimum only

For most borrowing above £3,000 that will take more than a year to repay, a personal loan offers more predictability and usually a lower rate than a standard credit card. The exception is a 0% purchase or balance-transfer deal — if you're certain you can clear the balance within the promotional period, a 0% card beats any personal loan rate.

Read our companion guide on credit card interest: How Credit Card Interest Builds Up.

See the true cost of your loan

Enter any UK loan to see monthly payments, total interest, amortisation table and overpayment savings.

Loan Repayment Calculator → Credit Card Calculator →

Frequently Asked Questions

Why does so much of my early loan payment go to interest?

This is amortisation. Your monthly payment is fixed, but in month one interest is charged on the full loan balance — so the interest portion is at its peak. As you reduce the balance month by month, the interest charge falls and more of each payment clears principal. By the final months, almost the entire payment is principal. This is normal and unavoidable on any standard repayment loan.

What does APR actually mean on a loan?

APR (Annual Percentage Rate) is the standardised annual cost of borrowing, including interest and any mandatory fees. UK lenders must quote it so you can compare products on a like-for-like basis. The "representative APR" is offered to at least 51% of accepted applicants — your personal rate may be higher. Always compare the total amount repayable rather than just the monthly payment or the headline APR.

How much does extending a loan term cost in extra interest?

Significantly. On a £10,000 loan at 7.9% APR, a 3-year term costs £1,282 in interest while a 5-year term costs £2,149 — an extra £867 to reduce monthly payments by £111. Only extend the term if your budget genuinely requires lower monthly payments. The shortest affordable term always costs least in total.

Can I overpay a personal loan without penalty?

Yes. The Consumer Credit Act gives you the right to overpay or settle early at any time. Lenders can charge an early repayment charge (ERC) capped at 58 days' interest on the amount overpaid. This is almost always less than the interest you'd save — so overpaying is nearly always worthwhile. Check your agreement to confirm your specific ERC terms.

What is the difference between a personal loan and a credit card for borrowing?

Personal loans have a fixed monthly payment, fixed end date and usually lower APRs for amounts above £3,000. Credit cards have flexible payments, no fixed end date and higher standard APRs — though 0% deals can be very cheap for short-term borrowing. For amounts over £3,000 repaid over more than 12 months, a personal loan is usually cheaper. For smaller amounts or short periods, a 0% credit card often wins.