Calculate payments, affordability & Stamp Duty — US & UK
| Month | Payment | Principal | Interest | Balance |
|---|
🇺🇸 US Affordability: Uses the 28%/36% debt-to-income rule to find your maximum home price. Monthly payment includes principal, interest, taxes, and insurance (PITI).
🇬🇧 UK Affordability: Uses the standard 4.5× income multiple used by most UK lenders. Also calculates Stamp Duty Land Tax (SDLT) for England — including first-time buyer relief and the 5% surcharge for additional properties (rates from 1 April 2025).
🇬🇧 UK Repayment: Enter your mortgage amount, rate, and term to get monthly repayments and a full amortisation schedule. Add overpayments to see how much interest you save.
Results are estimates for informational purposes. Speak to a mortgage adviser before making financial decisions.
In the UK, most lenders offer between 4× and 4.5× your annual income. Some specialist lenders go up to 5–5.5× for high earners. In the US, lenders use the 28/36 rule: your mortgage payment should not exceed 28% of your gross monthly income, and your total debt payments should not exceed 36%. Your credit score, deposit size, and existing debts also affect how much you can borrow.
With a repayment mortgage, each monthly payment covers both interest and a portion of the loan balance, so the debt reduces over time and is fully paid off at the end of the term. With an interest-only mortgage, you only pay the interest each month — the full loan balance remains and must be repaid at the end of the term (usually through savings, investments, or selling the property). Repayment mortgages are far more common for residential buyers.
Stamp Duty Land Tax is a tax paid when buying property in England and Northern Ireland. From 1 April 2025, the rates are: 0% up to £125,000; 2% on £125,001–£250,000; 5% on £250,001–£925,000; 10% on £925,001–£1.5M; 12% above £1.5M. First-time buyers pay 0% up to £300,000 and 5% up to £500,000 (no relief above £500,000). Second homes and buy-to-let properties attract a 5% surcharge on top of standard rates on every band. Scotland (LBTT) and Wales (LTT) have different rates.
A fixed-rate mortgage locks in your interest rate for a set period (typically 2, 5, or 10 years), giving payment certainty regardless of base rate changes. A variable rate (tracker or SVR) moves with the Bank of England base rate, which can mean lower payments when rates fall but higher payments when they rise. Fixed rates suit buyers who want predictability; variable rates can save money when interest rates are falling.
The minimum deposit is typically 5% of the property price (for most residential mortgages). A 10% deposit gives access to significantly better rates. A 25% deposit or more typically gets you the best rates available. A larger deposit reduces your loan-to-value (LTV) ratio, which lenders use to price risk — the lower the LTV, the lower the interest rate offered.
📖 Related Guide
Income multiples, affordability stress tests, LTV tiers, what lenders really look at, and the full true cost of buying — before you talk to a broker.
Read the guide →Figures are estimates for guidance only. See about this site — how we source data and what these tools can and cannot do.
Monthly mortgage repayments use the standard annuity formula: M = P × [r(1+r)^n] / [(1+r)^n − 1], where P is the loan amount, r is the monthly interest rate (annual rate divided by 12), and n is the total number of monthly payments. Each payment covers that month's interest on the outstanding balance plus a portion of the principal, so the loan is fully repaid by the final payment.
In the early years, most of each payment covers interest rather than capital. On a £300,000 mortgage at 4.5% over 25 years, the first payment of roughly £1,666 includes approximately £1,125 of interest and just £541 of capital. By year 20, those proportions reverse. This is why frequent remortgaging or switching lenders can reset your repayment progress and extend the total interest paid.
Most UK lenders use an income multiple of 4–4.5 times gross annual income as the baseline for maximum borrowing. Some offer 5–5.5 times for high earners or certain professions, and specialist products exist up to 6 times in specific circumstances. Since the Mortgage Market Review (2014), lenders must stress-test affordability at rates typically 3% above the initial rate — meaning how much you can borrow depends not only on current income but on whether you could afford repayments if rates rose significantly.
Factors that reduce borrowing capacity include existing debts (car finance, credit cards, personal loans), dependants, and a history of missed payments. Factors that improve it include a larger deposit (lower LTV), strong and stable income, and a clean credit record. Joint applications use combined income but also combine all debts.
SDLT in England is charged in bands on the purchase price. From April 2025, the standard rates are: 0% up to £125,000; 2% from £125,001 to £250,000; 5% from £250,001 to £925,000; 10% from £925,001 to £1.5m; 12% above £1.5m. First-time buyers pay 0% up to £300,000 and 5% between £300,001 and £500,000 — no relief is available above £500,000. Second homes and buy-to-let properties attract a 5% surcharge on all bands.
Scotland uses Land and Buildings Transaction Tax (LBTT) and Wales uses Land Transaction Tax (LTT), each with different rate bands. Our dedicated stamp duty calculator covers all UK nations including first-time buyer relief, higher-rate surcharges, and mixed-use property rules.
A repayment mortgage gradually reduces the outstanding balance so the property is owned outright at the end of the term. An interest-only mortgage requires payments covering only the monthly interest — the full capital remains owed at the end and must be repaid separately, typically from an investment vehicle or property sale.
Interest-only monthly payments are roughly 40–50% lower for the same loan size and rate, but total interest paid over the term is substantially higher because the balance never reduces. Most lenders now require a credible repayment strategy before granting interest-only mortgages to owner-occupiers, and they are rarely available without significant equity.
US lenders typically apply the 28/36 debt-to-income rule. Housing costs (mortgage principal, interest, property tax, and homeowners insurance — PITI) should not exceed 28% of gross monthly income. Total debt obligations (housing plus car payments, student loans, credit cards, and other recurring debts) should not exceed 36%. Some loan programs (FHA, VA) allow higher ratios for qualifying borrowers.
The US 30-year fixed-rate mortgage is the most common home loan structure — it provides payment stability over a long period. 15-year mortgages carry higher monthly payments but build equity much faster and carry a lower interest rate, typically 0.5–0.75% below 30-year rates.
UK income multiples reflect standard lender criteria under Mortgage Market Review guidelines. SDLT rates are HMRC figures effective April 2025. US affordability follows CFPB published guidelines. Repayment calculations use standard annuity mathematics. Results are estimates — actual mortgage offers depend on individual lender assessment, credit scoring, and property valuation.
Researched and maintained by Iulian, founder of Flux Media Systems. General information, not professional advice — about this site & our sources →