Guarantor Loan Calculator
Free UK guarantor loan calculator. Enter the amount, representative APR and term to see your monthly repayment, total repayable and total interest — updated for 2025/26.
Last updated: June 2026
Guarantor Loan Calculator UK
Work out monthly repayments, total repayable and total interest on a guarantor loan
About This Calculator
This guarantor loan calculator is part of UK Calculator's suite of financial tools for UK residents. It applies the standard amortising loan formula used by FCA-regulated lenders so you can see the true monthly and total cost of a guarantor loan before you apply.
Why Use UK Calculator?
- Accurate: Uses the standard reducing-balance amortisation formula
- Free: No registration or payment required
- Privacy-focused: All calculations performed locally in your browser
- Mobile-friendly: Works on all devices
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Guarantor Loan Calculator UK: A Complete 2025/26 Guide
A guarantor loan lets someone with limited or poor credit history borrow money by having a trusted person — usually a parent, partner, family member or close friend — agree to repay the debt if they cannot. Because the lender has that extra security, it may approve an application it would otherwise decline. The trade-off is cost: guarantor loans carry some of the highest representative APRs in the regulated UK lending market, commonly between 39.9% and 49.9% APR, with the wider market stretching from around 30% up to 79.9% APR. This calculator and guide help both borrower and guarantor understand exactly what they are signing up for before any agreement is made.
Why run the numbers before you commit?
- See the real cost: a high APR means the interest can rival or exceed the amount borrowed over the term.
- Protect the guarantor: the guarantor is liable for the full balance if the borrower defaults — they need to see the worst-case figure.
- Compare offers properly: a lower monthly payment over a longer term usually means more total interest, not less cost.
- Plan affordably: the FCA requires lenders to assess affordability for both parties, and you should too.
How the Guarantor Loan Calculator Works
The calculator uses the standard amortising (reducing-balance) loan formula that FCA-regulated lenders use to set fixed monthly repayments. Every month you pay the same amount; part covers interest on the outstanding balance and the rest reduces the principal, so the interest portion shrinks over time. The formula is:
- M = the fixed monthly repayment.
- P = the principal (the amount you borrow).
- r = the monthly interest rate = representative APR ÷ 100 ÷ 12. For a 39.9% APR, r = 0.399 ÷ 12 = 0.033250.
- n = the total number of monthly payments = term in years × 12.
The calculator then multiplies the monthly repayment by the number of months to find the total repayable, and subtracts the amount borrowed to find the total interest. Everything runs in your browser in well under a millisecond, so results update the moment you press Calculate — and a default example is shown when the page loads. No data leaves your device.
A note on convention: the APR is the legally required headline cost figure and includes interest plus any compulsory fees. Our calculator treats your entered APR as the nominal annual rate divided into twelve equal monthly periods (APR ÷ 12), which mirrors how UK lenders quote and apply monthly instalments on personal and guarantor loans. If your agreement includes a separate one-off fee, add it to the principal to see its effect, or use our APR Calculator to convert between rates.
Worked Example: £5,000 Guarantor Loan at 39.9% APR
Let's walk through a realistic case using a typical guarantor loan representative APR. Suppose the borrower needs £5,000, the lender's representative APR is 39.9%, and the term is 3 years (36 months).
Step 1 — Find the monthly rate
r = 39.9 ÷ 100 ÷ 12 = 0.033250 (about 3.325% per month).
Step 2 — Find the number of payments
n = 3 years × 12 = 36 months.
Step 3 — Apply the formula
M = 5,000 × 0.033250 × (1.033250)36 ⁄ ((1.033250)36 − 1) = £240.26 per month.
Step 4 — Total cost
Total repayable = £240.26 × 36 = £8,649.33. Total interest = £8,649.33 − £5,000 = £3,649.33.
The headline lesson is stark: on a £5,000 guarantor loan at 39.9% APR over three years, you repay almost £3,650 in interest — roughly 73% of the amount borrowed. The same £5,000 over the same term at a mainstream 8% personal-loan APR would cost only about £640 in interest. That gap is exactly why this calculator exists: a guarantor loan can be the right answer when no cheaper credit is available, but you should only choose it with full sight of the total cost, and the guarantor should understand that this whole balance is the sum they are guaranteeing.
How term and APR change the cost of a £5,000 guarantor loan
| Scenario | Monthly Repayment | Total Interest | Total Repayable |
|---|---|---|---|
| £5,000 · 39.9% · 24 months | £305.67 | £2,336.05 | £7,336.05 |
| £5,000 · 39.9% · 36 months | £240.26 | £3,649.33 | £8,649.33 |
| £5,000 · 39.9% · 60 months | £193.43 | £6,605.58 | £11,605.58 |
| £5,000 · 49.9% · 36 months | £270.26 | £4,729.41 | £9,729.41 |
Key insight: stretching the same £5,000 loan from 24 to 60 months cuts the monthly payment by about £126 but more than doubles the interest (from roughly £2,464 to £6,096). With guarantor loans, the shortest term you can comfortably afford almost always costs far less overall.
What a Guarantor Is Actually Liable For
The single most important point: if the borrower stops paying, the guarantor must repay the entire outstanding balance — including interest and any charges. Being a guarantor is a serious, legally binding financial commitment, not a formality.
A guarantor loan is a regulated credit agreement under the Consumer Credit Act 1974 and falls under the supervision of the Financial Conduct Authority (FCA). The guarantor signs a separate guarantee promising to cover the debt. Key responsibilities and protections include:
- Full liability on default. If the borrower misses payments, the lender can require the guarantor to pay. The guarantor can be asked to clear the whole remaining balance, not just the missed instalment.
- A default notice first. Under FCA finalised guidance FG17/1, the lender must notify the guarantor of its intention to take payment, and give a genuine opportunity to pay, before collecting from the guarantor's account.
- Affordability checks for both parties. FCA rules require the lender to assess whether both the borrower and the guarantor can afford the repayments before lending.
- Impact on the guarantor's credit file. Missed payments and a recorded default can damage the guarantor's own credit score and future borrowing, even though they never spent the money.
- Possible court action. If the guarantee is called in and remains unpaid, the lender can pursue the guarantor through the courts, which may lead to a County Court Judgment (CCJ).
Anyone thinking of acting as a guarantor should read Experian's guide to being a guarantor and consider the worst case — could they afford this loan if they suddenly had to take it over entirely? If the honest answer is no, the guarantee should not be signed.
The Rules and Factors That Matter
Representative APR
By law, the advertised representative APR must be offered to at least 51% of accepted applicants. Your personal rate may be higher. Guarantor loan representative APRs are commonly 39.9%–49.9%, with the wider market spanning roughly 30%–79.9%.
14-Day Right to Withdraw
Under the Consumer Credit Act 1974, the borrower has a 14-day cooling-off period to withdraw from the credit agreement. You repay only the principal plus any interest accrued for the days the money was held.
Early Repayment
You can settle early. The lender may add an early settlement adjustment of up to 28 days' interest (up to 58 days for loans over 12 months), but the high APR means early repayment usually still saves money.
Typical Amounts & Terms
Guarantor loans typically range from about £500 to £15,000, repaid over 1 to 7 years. The guarantor is usually a homeowner or has a strong, stable income, aged 18+ and not financially linked to the borrower.
Wider context: the Bank of England base rate is currently 3.75% (held at the latest decision). The base rate influences mainstream loan pricing, but guarantor loan APRs are driven far more by credit risk than by the base rate — which is why they remain high even when the base rate is modest. Sources: Bank of England.
Cheaper Alternatives Worth Checking First
Because of the cost, a guarantor loan should usually be a considered choice rather than a first resort. Depending on your circumstances, these options may be significantly cheaper:
- Credit union loans — interest on credit union loans is capped (a maximum of 3% per month, around 42.6% APR) and most charge far less, often around 12.7% APR.
- 0% purchase or money-transfer credit cards — if your credit allows, an interest-free promotional period can be cheaper, provided you clear the balance before it ends.
- A standard personal loan — if you can wait and improve your credit score first, mainstream APRs of 6%–12% are dramatically cheaper.
- Debt consolidation — if the goal is to tidy up existing debts, model the numbers with our debt consolidation calculator before borrowing more.
- Free debt advice — MoneyHelper, StepChange and Citizens Advice offer free, impartial help if borrowing feels like the only way to cope.
Whatever you choose, compare the total amount repayable, never just the monthly figure. A low monthly payment over a long term can quietly cost far more than a slightly higher payment over a shorter one — as the comparison table above demonstrates.
How to Use This Guarantor Loan Calculator
Follow these four steps to estimate the true cost of a guarantor loan:
- Enter the loan amount – the total you wish to borrow in pounds (for example £3,000 or £7,500).
- Enter the representative APR – the rate quoted by the lender. Guarantor loans are commonly 39.9%–49.9% APR; use the exact figure from your quote where possible.
- Choose the term – your repayment period in months or years. Shorter terms cost more per month but far less in total interest.
- Review your results – the calculator instantly shows the monthly repayment, total repayable and total interest so you and your guarantor can see the full commitment.
Sources & Methodology
Official Resources
- FCA FG17/1 – Guarantor loans: default notices – sets out how lenders must notify guarantors before taking payment.
- FCA – Consumer guidance on loans and credit – your rights and how regulated lending works.
- Consumer Credit Act 1974 – the legislation governing regulated credit agreements, the 14-day right to withdraw and early settlement.
- Bank of England – Bank Rate – current base rate (3.75% at the latest decision).
- MoneyHelper – free, impartial guidance from the Money and Pensions Service.
Calculation Method
All results use the standard amortising loan formula M = P × r × (1+r)n ⁄ ((1+r)n − 1), with the monthly rate r = representative APR ÷ 100 ÷ 12 and n = the number of monthly payments. This is the reducing-balance method used by FCA-regulated lenders to set fixed monthly instalments.
Important Disclaimer
The APRs in our examples are representative APRs for illustration. Lenders must offer the advertised representative APR to at least 51% of successful applicants, but your actual rate may differ based on your circumstances and the lender's criteria. This calculator provides estimates only and is not financial advice. Always obtain a personalised quote and read the credit agreement in full before borrowing or agreeing to be a guarantor.