UK Mortgage Calculator Estimate repayments, Stamp Duty, affordability, and overpayment savings — with 2025 UK rates, FCA ...
UK Mortgage Calculator
Estimate repayments, Stamp Duty, affordability, and overpayment savings — with 2025 UK rates, FCA rules, and SDLT bands.
Repayment Formula**:
$$PMT = P \frac{r(1+r)^n}{(1+r)^n - 1}$$
Where: • $P$ = loan amount • $r$ = monthly rate (APR ÷ 12) • $n$ = total months
Example** (£255K loan @ 4.8%, 25 yrs): • Monthly = **£1,455** • Total interest = **£222,000**
Stamp Duty (England/Wales, 2025)**:
- 0% up to £250,000 (£425,000 FTB)
- 5% £250,001–£925,000
- 10% £925,001–£1.5M
- 12% over £1.5M
- +3% surcharge for second homes
✅ Pro Tip**: Always compare **APRC** (not just rate) — includes fees, insurance, and product length.
⚠️ Avoid these pitfalls:
- Early Repayment Charges (ERC)** — 1–5% in early years; check cliff dates
- “5x income” brokers** — non-FCA regulated; may ignore affordability
- Interest-only for residential** — banned by FCA unless strict criteria met
- Switching too early** — £1,500+ fees may outweigh rate savings
✅ Pro Tips**:
- Use **offset mortgages** for flexible overpayments (no ERC)
- Stress-test at **7.5%+** — FCA requirement for affordability
- Get Agreement in Principle (AIP) *before* making offers
| Scenario | Loan | Rate | Payment | SDLT |
|---|---|---|---|---|
| FTB £300K home | £255K | 4.8% | £1,455/mo | £0 |
| Second home £300K | £240K | 5.2% | £1,420/mo | £11,250 |
| Buy-to-Let £250K | £187.5K | 5.6% | £1,102/mo (IO) | £7,500 |
📉 Affordability Rules (FCA MMR)**:
- Max loan: **4.5x joint income**
- Stress test: **7.5%+ rate** (even if fixed at 4.5%)
- Outgoings: credit cards, loans, childcare, travel
➡️ Standard Mortgage
“£300K house, 15% down, 4.8% rate — what’s my payment?”
➡️ Affordability
“£65K income, £1.2K outgoings — how much can I borrow?” (FCA stress test)
➡️ Stamp Duty
“£300K first-time buyer vs. second home — what’s the SDLT?”
➡️ Overpayments
“£200/mo extra — how much time and interest do I save?”
Note: Uses 2025 SDLT bands, FCA 4.5x/7.5% rules, and typical UK mortgage products. Assumes no fees in base calc (add to loan for APRC).