UK Mortgage Calculators: Borrowing, Repayments, Stamp Duty and LTV

Five calculators sit on this page, and each answers a different question at a different stage of a mortgage decision. Borrowing range comes first for buyers, monthly cost for anyone refixing, stamp duty for second properties, rental cover for landlords and loan-to-value for anyone weighing a deposit against a rate band. Mortgage One is a whole of market mortgage adviser that turns these indicative figures into a lender-specific borrowing position for buyers, homeowners and landlords.

If the number a calculator gives you does not match what you think you can afford, call 01202 155992 or contact Mortgage One.

Which calculator answers the question you are actually asking?

Start with the decision in front of you, not the calculator you saw first. Buyers need a borrowing range, remortgagers need a monthly cost, landlords need rental cover at a 145% stress test, and anyone within 5% of an LTV band boundary needs the loan-to-value figure before anything else.

●      How Much Can I Borrow? Mortgage Calculator. Enter income, outgoings and deposit to get an indicative lending range you can take into a viewing or an agreement in principle.

●      Mortgage Repayment Calculator. Work out monthly cost by loan size, interest rate and term, on either a capital repayment or interest-only basis.

●      Stamp Duty Calculator. Estimate SDLT at current rates, including first-time buyer relief and the surcharge on additional and buy-to-let property.

●      Buy-to-Let Mortgage Calculator. Run the rental stress test lenders use to size a buy-to-let loan, with rental cover and loan-to-value cross-checks.

●      Loan-to-Value (LTV) Calculator. Turn property value and deposit into an LTV percentage and the rate band it falls in, plus the deposit needed to reach the band below.

Running two or three in sequence is more useful than running one in isolation. A borrowing range with no loan-to-value check tells you what a lender might advance but nothing about the rate band you would land in, and a monthly payment figure with no stamp duty estimate leaves the largest single upfront cost out of the budget.

How much can I borrow before a lender says no?

Most UK lenders start at 4 to 4.5 times gross annual income, with 5 to 5.5 times available to qualifying applicants and 6 times reserved for higher earners or specific professions. The affordability assessment then cuts that figure down for credit commitments, dependants and stress-tested payments.

The income multiple is the ceiling, not the answer. It sets the largest loan a lender will consider before any of your circumstances are taken into account, and the affordability model then works downwards from it. Car finance, credit card balances, childcare and student loan deductions all reduce the surplus the lender is prepared to commit to a mortgage payment, which is why two applicants on the same salary can be offered figures £60,000 apart. Our guide to mortgage income multiples sets out which lenders stretch furthest and what they require in exchange.

A borrowing calculator gives you a range because that is the honest output. Treat the top of the range as a lender-specific outcome that needs the right lender, not a number every lender will match. If the range comes back well below the property prices you are looking at, the useful next steps are usually clearing a commitment, extending the term, adding a second applicant or finding a lender with a more generous treatment of bonus, commission or overtime income.

Working out monthly repayments and total interest

A £200,000 repayment mortgage at 5% over 25 years costs around £1,169 a month and about £150,800 in interest across the term. Stretch the same loan over 35 years and the monthly figure falls to roughly £1,009, but total interest rises to around £223,900.

The interest rate is the single largest variable. On that same £200,000 over 25 years, moving from 5% to 4% cuts the monthly payment to about £1,056 and the total interest to roughly £116,700, a difference of around £34,100 across the term for one percentage point. That is the practical reason the loan-to-value check matters before the rate comparison: the band you sit in decides which rates you are even quoted.

Term length works the other way. A longer term is a legitimate tool for passing an affordability assessment, but it is expensive if left in place, so it is worth shortening at each remortgage once income allows. Our guide to understanding mortgage repayments covers capital repayment against interest-only, part-and-part arrangements and what happens when a fixed deal ends.

Most products allow overpayments of up to 10% of the outstanding balance each year without an early repayment charge. Modelling an overpayment alongside the base repayment figure usually shows a larger saving than borrowers expect, because every pound of capital cleared early removes interest from every remaining month of the term.

Stamp duty on a purchase, second home or buy-to-let

Standard SDLT in England and Northern Ireland starts at 0% to £125,000, then 2% to £250,000 and 5% to £925,000. First-time buyers pay nothing to £300,000, with relief lost entirely above £500,000. Additional property adds 5 percentage points to every band above £40,000.

The tax is charged in slices, not on the whole price at one rate. A £300,000 main residence attracts nothing on the first £125,000, 2% on the next £125,000 and 5% on the final £50,000, giving £5,000 in total. The same £300,000 bought as a second home or a rental carries the 5 percentage point surcharge on every slice, taking the bill to £20,000. That £15,000 gap is the number most landlords underestimate when they size a deposit.

First-time buyer relief has a hard edge rather than a taper. A first-time buyer at exactly £500,000 pays £10,000. At £500,001 the relief disappears completely and the bill becomes £15,000, so a single pound over the threshold costs £5,000. Where the purchase is a holiday home or a property for a family member, our guide to second home mortgages covers the deposit and affordability treatment that sits alongside the tax.

Scotland and Wales operate their own systems, Land and Buildings Transaction Tax and Land Transaction Tax, with different bands and different additional property supplements. If the property is north of the border or in Wales, take the figure from the relevant national calculator rather than the SDLT tables.

For a free initial consultation that puts a real purchase cost, deposit and borrowing figure against your case, call 01202 155992 or contact Mortgage One.

Rental stress testing before a buy-to-let application

Buy-to-let borrowing is sized by interest coverage ratio, not salary. The PRA baseline is 125% cover at a stress rate of at least 5.5%, but lenders commonly apply 145% for higher-rate taxpayers and 160% to 175% for additional-rate taxpayers, HMOs and limited company cases.

The maths decides the loan before the headline rate does. On a £200,000 interest-only loan stressed at 5.5%, the notional annual interest is £11,000. At a 145% ICR the lender needs gross rent of £15,950 a year, or £1,329 a month. At 125% the same loan needs £13,750, or £1,146 a month. A property renting at £1,200 clears the second test and fails the first, on identical borrowing.

That is why the lender shortlist matters more on a buy-to-let than on a residential case. Taxpayer status, ownership structure, property type and fixed rate length all change the ICR and the stress rate applied, and a five-year fix frequently allows a lender to stress at pay rate rather than 5.5%, which can lift the workable loan materially. Our buy-to-let mortgage guide sets out how the criteria differ across the market.

Once you hold four or more distinct mortgaged rental properties, lenders treat you as a portfolio landlord and assess the whole portfolio rather than the single property being financed. At that point a calculator output is only a starting point, because the lender is modelling aggregate rental cover, gearing and cash flow across every property you own.

How much does your loan-to-value band change the rate?

Lenders price in loan-to-value bands, typically at 60%, 75%, 80%, 85%, 90% and 95%. A borrower sitting at 90.4% pays the 95% band price, so finding the extra deposit that drops you under 90% can be worth more than shopping a different lender.

The bands are cliffs, not slopes. Being fractionally the wrong side of one costs the whole band difference, and a down-valuation can push you across without any change to your deposit. A £250,000 purchase with a £25,000 deposit is a £225,000 loan at 90% LTV. If the valuation comes back at £245,000 the loan-to-value becomes 91.8% and the case reprices into the 95% band unless you find more deposit or renegotiate the price.

The same arithmetic works in your favour on a remortgage. Capital repaid over a fixed term plus any growth in the property value can move a case from 85% to 75% without a penny of new deposit, which is usually the single biggest lever on the new rate. Most lenders let you secure a new deal up to six months before the current one ends, so run the loan-to-value figure early and read it alongside our remortgaging guide before deciding between a product transfer and a full switch.

Where a calculator stops and lender criteria begin

A calculator applies one set of assumptions. A lender applies its own income treatment, credit policy, property rules and maximum age at term end, which is commonly between 70 and 85. Two applicants with identical salaries routinely receive offers that differ by tens of thousands of pounds.

The gap sits mostly in income treatment. One lender takes 100% of a contractual bonus, another averages three years, another caps it at 50%. Overtime may need six months of evidence at one lender and twelve at the next. Self-employed applicants can be assessed on the latest year, a two-year average or salary plus dividends, and the answer changes the loan by a wide margin. Foreign currency income narrows the panel again, often with a haircut applied to the converted figure.

Property is assessed as well as the borrower. Flats above commercial premises, short leases, high-rise ex-local authority blocks and non-standard construction all reduce the lender pool or cap the maximum loan-to-value, regardless of how strong the affordability looks.

●      This information is a guide only and should not be relied on as a recommendation or advice that any particular mortgage is suitable for you.

●      All mortgages are subject to the applicant(s) meeting the eligibility criteria of lenders.

●      Make an appointment to receive mortgage advice suitable for your needs and circumstances.

If a calculator result and a lender decision have already diverged on your case, the reason is almost always a criteria point rather than the arithmetic. Our guide to mortgage lending criteria explains what lenders assess and where the differences between them tend to sit.

To have your income, deposit and property tested against live lender criteria rather than a generic calculation, call 01202 155992 or contact Mortgage One.

Back to Mortgage Guides

The information provided in this article is for general guidance only and does not constitute personal or regulated financial advice. If you’d like to understand what these moves could mean for you, speak to Mortgage One. We can explain your options and timings based on your specific circumstances.

FAQs

1. Which mortgage calculator should I use first?

Start with the calculator that matches the decision in front of you. Buyers usually need the borrowing range first, remortgagers need the monthly repayment and loan-to-value figures, and landlords need the rental stress test before anything else. Running the loan-to-value calculator alongside whichever one you start with is almost always worthwhile, because the band you fall into affects the rates available to you.

2. How much can I borrow on a mortgage calculator?

Most calculators apply an income multiple of around 4 to 4.5 times gross annual income and then reduce it for outgoings and existing commitments. Some lenders will stretch to 5, 5.5 or 6 times income for applicants meeting specific criteria on income level, deposit or profession. A calculator cannot know which of those lenders would accept your case, so treat the top of the range as conditional.

3. Are mortgage calculator results accurate?

They are useful estimates rather than lending decisions. The final outcome depends on the individual lender’s affordability model, how it treats your income, your credit profile, the property, fees and the supporting documents you can provide. Two lenders assessing the same case regularly produce different maximum loans.

4. Can I use these calculators for remortgaging?

Yes. The repayment and loan-to-value calculators are the two that matter most at remortgage, because capital repaid and any change in property value can move you into a lower band and a better rate. Most lenders allow a new deal to be secured up to six months before the current one ends, so running the figures early is worthwhile.

5. Do buy-to-let calculator results match lender stress tests?

No, they are indicative only. Each lender sets its own interest coverage ratio, stress rate, minimum income and loan-to-value cap. A case that clears a 125% ICR at one lender can fail a 145% ICR at another on identical rent and borrowing, which is why the lender shortlist is chosen before the application rather than after it.

6. Is a decision in principle the same as a mortgage offer?

No. A decision in principle is an early indication based on limited information and usually a credit search. A formal mortgage offer follows a full application, underwriting, document checks and a valuation of the property. An agreement in principle can still be followed by a decline at full application.

7. Do expat and seafarer cases need a different approach?

Usually yes. Residency, country of residence, income currency, contract type and how your documents are formatted all narrow the lender panel, and mainstream calculators do not model any of it. Our guidance on expat mortgages and seafarer mortgages covers how lenders treat those cases.

8. When is it worth speaking to a broker rather than running another calculation?

When the number you need is not the number the calculator returns. If the borrowing range falls short of the property price, the rental cover fails the stress test, the loan-to-value sits just the wrong side of a band, or your income is anything other than a straightforward salary, the useful next step is matching the case to a lender whose criteria fit rather than repeating the arithmetic.