Monthly payments, the rate after your deal, and Stamp Duty in one place.
Who this is for: Buying or remortgaging a home in the UK.
£
£
15.0% of the price
%
years
Your deal5-year deal, then 7.25%
%
Your lender's standard variable rate (SVR), unless you remortgage.
Stamp Duty£5,000 (England & NI rates)
OverpaymentsNone
£
Many fixed deals let you overpay up to 10% of the balance a year without an early repayment charge.
Stamp Duty by band
Effective rate 1.67% of the price.
Portion of the price
Rate
Taxed amount
SDLT
£0 – £125,000
0%
£125,000
£0
£125,000 – £250,000
2%
£125,000
£2,500
£250,000 – £300,000
5%
£50,000
£2,500
How the payment is worked out
1Loan£300,000 − £45,000 = £255,000
2Monthly rate i and number of payments ni = 4.50% ÷ 12 = 0.3750% n = 25 × 12 = 300
3Payment = L × i ÷ (1 − (1 + i)^−n)£255,000 × 0.003750 ÷ (1 − 1.003750^−300) = £1,417.37
4After the 5-year dealBalance £224,038 re-spread over 20 years at 7.25% = £1,770.74 a month
Year-by-year schedule
How each year's payments split between interest and the balance you owe.
Year
Paid
Principal
Interest
Balance
1
£17,008
£5,649
£11,359
£249,351
2
£17,008
£5,909
£11,100
£243,442
3
£17,008
£6,180
£10,828
£237,262
Calculated in your browser — the numbers you enter are never sent to our servers.
Work out your monthly mortgage payment in pounds, what it becomes when your fixed deal ends, the Stamp Duty on the purchase and the cash you need on completion day. Switch between repayment and interest-only, add overpayments, and see the year-by-year balance.
Best for: First-time buyers, Home movers, Remortgage planning, Buy-to-let deposits
Updated September 2026 · Estimates only, not financial advice.
A £1,417 payment that becomes £1,771 when the five-year fix runs out
Most UK mortgages start on an initial rate — a two- or five-year fix, or a tracker — and then revert to the lender’s standard variable rate (SVR). The calculator works out the payment for the deal period first, then takes the balance that is left and re-spreads it over the remaining years at the rate you enter for afterwards. That is how lenders recalculate it too.
M = L × i ÷ (1 − (1 + i)^−n)
In the example on this page, £255,000 over 25 years at a 4.5% five-year fix costs £1,417.37 a month. After five years you still owe £224,037.65. At a 7.25% reversion rate the payment on that balance, spread over the remaining 20 years, is £1,770.74 — about £353 a month more. If you let it run to the end of the term, total interest comes to £255,019.92, against £170,211.85 had 4.5% lasted the whole 25 years.
The gap is the cost of staying put. Most borrowers remortgage or switch to a new product with the same lender before the deal ends, which is why the reversion rate matters mainly as the number to beat. Put your lender’s current SVR in the second rate box and you can see exactly what doing nothing would cost.
Stamp Duty on a £300,000 home: £5,000, £0 or £20,000 depending on who buys it
Stamp Duty Land Tax is charged in slices. Each band’s rate applies only to the part of the price inside that band, so a higher price never pushes the whole amount into a higher rate. The calculator uses the residential rates for England and Northern Ireland that have applied since 1 April 2025.
A home mover buying at £300,000 pays nothing on the first £125,000, 2% on the next £125,000 (£2,500) and 5% on the last £50,000 (£2,500): £5,000 in all. A first-time buyer pays nothing at all, because first-time buyer relief makes the first £300,000 tax-free. Someone buying it as a second home or buy-to-let pays £20,000, because the 5% surcharge on additional properties applies to every band, including the one that is otherwise 0%. A buyer who is not UK resident pays a further 2% on the whole price — £11,000 as a home mover.
First-time buyer relief has a hard edge. Up to £500,000, the first £300,000 is tax-free and the rest is taxed at 5%. Above £500,000 the relief disappears entirely and the standard rates apply to the whole price: a first-time buyer at £450,000 pays £7,500, but at £550,000 pays £17,500. The calculator flags when your price has crossed that line. Stamp Duty is due, with a return to HMRC, within 14 days of completion; your conveyancer normally files and pays it.
Up to £125,000 — 0% (first-time buyers: 0% up to £300,000)
£125,001 to £250,000 — 2%
£250,001 to £925,000 — 5% (first-time buyers: 5% from £300,001 to £500,000)
£925,001 to £1.5 million — 10%
Above £1.5 million — 12%
Additional properties: add 5 points to every band; non-UK residents: add 2 points
Why a 15% deposit puts you in the 85% LTV band, and what the next band is worth
Loan-to-value is the loan as a share of the property’s price or valuation. Lenders price mortgages in bands — commonly 60%, 75%, 80%, 85%, 90% and 95% — and each step down usually unlocks a lower rate, because the lender has more of a cushion if prices fall. The result panel shows your LTV and the band it sits in.
The example’s £45,000 deposit on £300,000 is 15%, so the £255,000 loan is exactly 85% LTV. Adding £15,000 to the deposit would bring it to 80%. Whether that is worth doing depends on the rate difference between the two bands on the day you apply; put both rates into the calculator and compare the monthly payments and total interest side by side.
Remember that LTV falls as you repay and as prices rise. When your deal ends, the band you remortgage into depends on the balance left and a fresh valuation — a reason the balance at the end of the deal is worth knowing in advance.
Interest-only costs £956 a month here — and leaves the whole £255,000 still owed
On an interest-only mortgage each monthly payment covers only the interest. At 4.5% on £255,000 that is £956.25 a month, £461 less than the repayment mortgage. But nothing is repaid: after 25 years you have paid £286,875 in interest and still owe the full £255,000.
Because of that, lenders offer interest-only only when you can show a credible way to repay the capital — an investment, pension lump sum or the sale of another property — and they usually ask for a larger deposit. Switch the toggle at the top of the calculator to see both versions of the same loan; the result panel shows the capital still owed at the end.
Overpaying £200 a month clears this mortgage four years sooner and saves £57,916
An overpayment goes straight off the balance, so every later month charges interest on a smaller amount. Add £200 a month to the example mortgage and it is paid off 49 months early, saving £57,915.98 in interest, because the smaller balance also shrinks the payment the lender recalculates when the fixed deal ends.
Check your offer before you overpay. During a fixed or discounted deal many lenders let you overpay up to 10% of the balance each year without an early repayment charge; beyond that, charges of a few percent of the excess can apply. Once you are on the standard variable rate, overpayments are usually unrestricted.
Scotland, Wales, fees and daily interest sit outside this calculator
Stamp Duty Land Tax applies in England and Northern Ireland only. Scotland charges Land and Buildings Transaction Tax and Wales charges Land Transaction Tax, each with its own bands and reliefs, so for a property there use Revenue Scotland’s or the Welsh Revenue Authority’s calculator for the tax and this one for the mortgage.
The mortgage figures are the standard monthly repayment method. Some lenders calculate interest daily, and arrangement fees, valuation fees, broker fees and early repayment charges all add to the true cost of a deal — compare offers on their annual percentage rate of charge (APRC) as well as the headline rate. This is an estimate for planning, not a mortgage offer; your lender’s European Standardised Information Sheet (ESIS) is the figure to rely on.
Worked example
A £300,000 home with a £45,000 deposit, a 4.5% five-year fix reverting to 7.25%, over 25 years, bought by a home mover.
Worked example
Loan (85% LTV) = £255,000
Monthly payment for 5 years = £1,417.37
Balance when the deal ends = £224,037.65
Payment at 7.25% afterwards = £1,770.74
Stamp Duty = £5,000
Limitations
Stamp Duty uses the England and Northern Ireland rates; Scotland (LBTT) and Wales (LTT) have their own bands.
Lender fees, early repayment charges, and the daily interest some lenders charge are not modelled.
The rate after your deal is held constant; real standard variable rates move with the Bank Rate.
Frequently Asked Questions
How much Stamp Duty will I pay?
In England and Northern Ireland a home mover pays 0% on the first £125,000, 2% up to £250,000, 5% up to £925,000, 10% up to £1.5 million and 12% above. On a £300,000 home that is £5,000. First-time buyers pay nothing up to £300,000 and 5% up to £500,000.
What happens when my fixed rate ends?
Unless you remortgage or take a new deal, the lender moves you to its standard variable rate. The calculator re-spreads the balance left over the rest of the term at that rate, so you can see the new payment.
Is interest-only cheaper?
The monthly payment is lower because none of it repays the loan, but you still owe the full amount at the end and pay more interest overall. Lenders will want to see a credible plan to repay the capital.
Sources & References
Figures on this page are checked against primary, authoritative sources. Links open in a new tab.
Results are estimates based on the figures you enter and standard formulas. Rates, fees, taxes, and lender terms vary and change over time, so confirm important numbers with your lender or a qualified professional. This is educational information, not financial advice.
Published a UK mortgage calculator split out of the US one: repayment and interest-only, an initial deal followed by the reversion rate, and overpayments.
Stamp Duty Land Tax for England and Northern Ireland at the rates from 1 April 2025, with first-time buyer relief and the additional-property and non-resident surcharges.
Added an automated formula suite checked against HMRC’s published bands and hand-computed payments.
Show it to your clients, not just tell them
Mortgage brokers, accountants, and advisors embed this to walk clients through the numbers live — nothing they enter ever leaves their browser.