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Mortgage Calculator

UK-style mortgage maths plus optional full-picture costs: England and NI stamp duty (SDLT), fees, renovation budget and value add, or a custom purchase-tax rate outside the UK. Monthly payment, total interest, LTV, cash upfront, amortisation table.

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Calculator

Use 20% or 50000

Loan / LTVn/a
Monthly paymentn/a
Total interestn/a
Total repaidn/a
Interest saved by overpayn/a
Term with overpayn/a
Year-end amortisation
YearInterestCumulative interestBalance
The full picture: costs beyond the mortgage

Optional. Leave closed and the mortgage figures above stay unchanged. England and Northern Ireland SDLT rates as of 1 April 2025 (still current Nov 2026). Scotland (LBTT) and Wales (LTT) differ and are not modelled. Non-UK buyers can pick Custom rate.

Legal, survey, broker. Default 0
What you think the works add to market value
Stamp duty (SDLT)n/a
Total cash needed upfrontn/a
Post-renovation valuen/a
Equity after renovationn/a
Net value createdn/a
LTV before / after renovationn/a

Net value created = value added − renovation − purchase tax − fees (product + other).

SDLT band breakdown (England and NI)
BandRateTaxableTax

Rates source: gov.uk residential SDLT, higher rates page updated 1 April 2025. First-time buyer relief: 0% to £300,000 and 5% from £300,001 to £500,000; no relief if price is over £500,000. Additional property surcharge: 5 percentage points on each band. Not advice.

Real terms: do you actually make money?

Optional. Compares nominal pounds to today's purchasing power. Ignores rent you would otherwise pay, maintenance, insurance and tax on gains. Selling costs are included via the input below (default 0%).

Used to deflate future cash into today's money
Blank = mortgage term
e.g. 2 for agent + legal. Included in the bottom line
Property value at end (nominal)n/a
Property value at end (today's money)n/a
Mortgage payments (nominal total)n/a
Mortgage payments (today's money)n/a
Bottom line gain (nominal)n/a
Bottom line gain (today's money)n/a
Real annualised return on cashn/a

Bottom line = (end property value − remaining loan − selling costs) minus (upfront cash + all mortgage payments made). Upfront cash uses deposit plus any tax/fees/renovation from the full-picture section (0 if left blank). Each future cashflow is deflated by inflation for the real figure. Fixed mortgage payments shrink in real terms when inflation is positive.

Opportunity cost: house vs investing

Optional. Puts the same cash into markets instead of buying. Rent matters: a buyer stops paying rent; an investor still pays it. Enter the rent you would pay instead so monthly investing equals mortgage payment minus rent. Ignores tax wrappers, dividend tax and leverage risk. Past returns are not a forecast.

Reduces the investor's monthly contribution. 0 = ignore rent
Default 10.0%: Damodaran S&P 500 total return CAGR 1928-2025
Default 4.5%: Damodaran US 10-year T.Bond total return CAGR 1928-2025 (long-bond proxy; not a 25-year series)
Default 7.8%: 60% S&P + 40% 10y T.Bond blend of those CAGRs

S&P 500

End portfolion/a
End housing equityn/a
Difference (portfolio − house)n/a
Same in today's moneyn/a

Long US Treasuries (10y proxy)

End portfolion/a
End housing equityn/a
Difference (portfolio − house)n/a
Same in today's moneyn/a

60/40 stocks and bonds

End portfolion/a
End housing equityn/a
Difference (portfolio − house)n/a
Same in today's moneyn/a

Defaults from Aswath Damodaran, Historical Returns on Stocks, Bonds and Bills, NYU Stern, annual total returns 1928-2025 (updated Jan 2026). Geometric (CAGR) means: S&P 500 ≈ 10.0%, US 10-year T.Bond ≈ 4.5%. 60/40 is 0.6×10.0 + 0.4×4.5. Editable. Housing equity = grown house value − selling costs − outstanding loan. Monthly market contributions = mortgage payment − rent.

How is a UK repayment mortgage payment calculated?

Monthly payment = loan × r(1+r)^n ÷ ((1+r)^n − 1), with r = annual rate ÷ 12 and n = years × 12.

What stamp duty rates does this use?

England and NI residential SDLT from 1 April 2025 (standard, first-time buyer, and +5pp additional-property bands). Scotland and Wales are not modelled.

Where do the S&P and Treasury return defaults come from?

Damodaran 1928–2025 total-return CAGRs: S&P 500 about 10.0%, US 10-year T.Bond about 4.5%. Editable; not a forecast.

The formula

Loan = price − deposit
Monthly rate r = annual rate ÷ 12; n = years × 12
Repayment payment = loan × r(1+r)^n ÷ ((1+r)^n − 1)
Interest-only payment = loan × r
LTV = loan ÷ price (and loan ÷ post-renovation value after works)
England and NI SDLT (from 1 Apr 2025): 0% to £125k, 2% to £250k, 5% to £925k, 10% to £1.5m, 12% above. Additional property adds 5 points on each band. First-time buyers: 0% to £300k and 5% to £500k; no relief above £500k.
Custom (non-UK): purchase tax = price × rate + fixed amount.
Cash upfront = deposit + purchase tax + other fees + product fee + renovation.
Net value created = value added − renovation − purchase tax − fees.
Overpayments cut interest and can shorten the term; we re-run the balance month by month.
Real terms: end house value and payments deflated by inflation; bottom line = (end value − loan − selling costs) − (upfront + payments), nominal and real.
Opportunity cost: invest the same upfront cash and (mortgage payment − rent) each month at an assumed return (S&P 500, US 10y T.Bond proxy, or 60/40). Compare end portfolio to housing equity.

Worked example

£200,000 loan, 5% annual, 25 years, repayment mortgage.

Monthly payment ≈ £1,169.18.

Total repaid ≈ £350,754. Total interest ≈ £150,754.

You pay about 75% of the borrowed amount again in interest over the life.


Full picture (optional): £500,000 home, £100,000 deposit (£400,000 loan), England and NI home mover, £30,000 renovation, £60,000 value add, fees £0.

SDLT ≈ £15,000. Cash upfront ≈ £145,000. Post-reno value £560,000. Equity after reno £160,000. Net value created ≈ £15,000. LTV 80.0% → 71.4%.

Methodology

How it calculates

  • UK-style amortising (or interest-only) payment from price, deposit, rate and term.
  • Optional full-picture block adds England/NI SDLT bands, fees, renovation and opportunity-cost defaults.

Formula

Loan = price − deposit
Monthly rate r = annual rate ÷ 12; n = years × 12
Repayment payment = loan × r(1+r)^n ÷ ((1+r)^n − 1)
Interest-only payment = loan × r
LTV = loan ÷ price (and loan ÷ post-renovation value after works)
England and NI SDLT (from 1 Apr 2025): 0% to £125k, 2% to £250k, 5% to £925k, 10% to £1.5m, 12% above. Additional property adds 5 points on each band. First-time buyers: 0% to £300k and 5% to £500k; no relief above £500k.
Custom (non-UK): purchase tax = price × rate + fixed amount.
Cash upfront = deposit + purchase tax + other fees + product fee + renovation.
Net value created = value added − renovation − purchase tax − fees.
Overpayments cut interest and can shorten the term; we re-run the balance month by month.
Real terms: end house value and payments deflated by inflation; bottom line = (end value − loan − selling costs) − (upfront + payments), nominal and real.
Opportunity cost: invest the same upfront cash and (mortgage payment − rent) each month at an assumed return (S&P 500, US 10y T.Bond proxy, or 60/40). Compare end portfolio to housing equity.

Assumptions

  • England and NI residential SDLT only in the full-picture block (from 1 Apr 2025). Scotland (LBTT) and Wales (LTT) are not modelled.
  • Opportunity-cost defaults are Damodaran historical CAGRs (editable), not forecasts.
  • No early repayment charges or lender stress tests.

Edge cases

  • First-time buyer SDLT relief applies only if price ≤ £500,000; above that, standard bands apply.
  • Additional-property mode adds 5 percentage points on each standard band.
  • Interest-only payments leave the principal outstanding.

Sources

Last checked:

FAQ

Does the optional section change the mortgage payment?

No. Leave it closed and the payment, interest and amortisation stay the same. Open it only when you want stamp duty, cash upfront or renovation maths.

Which stamp duty rates are used?

England and Northern Ireland residential SDLT as of 1 April 2025 (still current as of November 2026), including first-time buyer relief and the 5% additional-property surcharge. Scotland (LBTT) and Wales (LTT) are not modelled. Outside the UK, pick Custom rate and enter a flat % plus optional fixed amount.

Does this include UK fees, ERC or product rates?

The core maths is repayment only. The optional section lets you add product fees, legal/survey/broker fees, SDLT or a custom purchase tax, and a renovation budget. Early repayment charges and lender stress tests are not modelled.

Interest-only: do I still owe the principal?

Yes. Interest-only payments cover interest. The loan balance stays until you repay it another way.

Where do the S&P and Treasury return defaults come from?

Aswath Damodaran (NYU Stern) historical total-return CAGRs for 1928-2025: S&P 500 about 10.0%, US 10-year T.Bond about 4.5%. The 60/40 default is a 60/40 blend of those. They are editable. Past returns are not a forecast. The bond series is a 10-year proxy, not a 25-year yield.

Does opportunity cost include rent?

Only if you enter monthly rent you would pay instead. That amount is subtracted from each mortgage payment before it is invested in the market alternative. A buyer avoids rent; an investor does not.

Sources

Rates, rules or specs last checked 1 Nov 2026. Confirm on the official page before you act.

Popular variants

Same maths, aimed at a specific search. Pre-filled where it helps.

Not financial advice. This calculator is for education only. Double-check results before you make money decisions. Past moves do not predict future ones.