Mortgage Calculator UK

Mortgage Calculator UK: Repayment, Interest-Only, Buy-to-Let and Commercial

Use this mortgage calculator UK tool to calculate payments accurately for the particular type of mortgage you are actually dealing with and not a generic repayment formula stretched to fit everything. A repayment mortgage, an interest-only arrangement, a buy-to-let purchase, and a commercial loan are all really different calculations, and a mortgage repayment calculator UK constructed around one delivers a deceptive response applied to the others. 

Even if the arithmetic is right, if somebody is looking for a buy-to-let number and they receive back a conventional payback calculation, they have been handed the incorrect instrument for the task. This article covers all four varieties, each with its own reasoning and a worked example on a shared home, and then affordability and overpayment, the two questions that cut across every type of mortgage you’re actually taking out.

The Property We’ll Use

Let’s take one house to the equivalent portions: £350,000 to buy, £87,500 deposit at 25%, and £262,500 to finance. We will illustrate a general market positioning of 5% for a 5-year fixed period and a 25-year term where applicable, as of August 2026. The actual rates will depend on your deposit, your credit profile, and the lender you choose. See a current, dated rate comparison rather than rely on this illustrative figure.

Repayment Mortgage Calculator UK

The usual is a repayment mortgage (also known as capital and interest). Each monthly payment is part interest and part repayment of the loan, so the loan balance gradually reduces to zero at the end of the period.

M = P x [r(1+r)^n] / [(1+r)^n – 1 ]

On our 5% £262,500 mortgage over 25 years (300 months):

M = £262,500 × [0.004167 × (1.004167)³⁰⁰] ÷ [(1.004167)³⁰⁰ − 1] ≈ £1,535 per month.

Interest over the full duration of 25 years will amount to some £197,940.

Here’s the UK structure that catches folks out who are used to US mortgages. This rate is normally fixed for an initial time, in our example, 5 years, not the full 25-year term. When that fixed period finishes, the mortgage reverts to the lender’s standard variable rate (SVR) until you remortgage to a new agreement, and that SVR tends to be a lot higher. At the end of our 5-year fixed period, the outstanding balance is around £232,499, down from the original £262,500. That sum left over is what you would be renewing or remortgaging at whatever rate is available then.

This is something to build into your plans, not to deal with as a one-time item. Most UK borrowers will go through many fixed-rate cycles throughout the course of a mortgage, remortgaging every few years rather than locking in one rate for decades the way a US 30-year fixed-rate borrower might. One of the most dependable methods UK borrowers avoid overpaying without noticing it is by shopping around at the conclusion of each fixed period, rather than having the mortgage calculator UK quietly roll onto the lender’s SVR.

Interest Only Mortgage Calculator UK

A debt that only pays interest works very differently. Each monthly payment only covers the interest, so you don’t pay down any capital. The full loan balance stays due for the whole term.

Balance x monthly rate = monthly payment

For the same loan of £262,500 at 5%:

Each month, the payment is £1,094 (£262,500 x 0.004167).

That’s a lot less than the £1,535 payback amount. But the more important number is this: if the rate stayed the same for the whole 25 years, the total interest paid would be around £328,125, but the original amount of £262,500 would still be due because no money was ever put toward the capital.

To get to the heart of the matter, an interest-only mortgage needs a solid way to pay back the £262,500 balance when the term is over. This could be a separate savings plan, an investment, or a planned sale of an asset. Before giving you a mortgage, lenders check to see if you have a real plan for this. If the borrower doesn’t pay back the loan by the end of the time, they may have to sell the property to pay off the debt. Interest-only loans are now much more popular in buy-to-let than in residential lending. This is because the sale of the property is usually the only way to pay back the loan, making the repayment plan much more scrutinized by lenders.

Buy to Let Mortgage Calculator UK

Buy-to-let mortgages are not evaluated the same way that home mortgages are. Instead of comparing your personal income to a multiple of that income, lenders use something called an interest coverage ratio (ICR) to see if the property’s predicted rental income is enough to cover the mortgage interest.

Lenders usually need rental income to cover the mortgage interest by 125% for basic-rate taxpayers and limited company borrowers, or 145% for higher-rate taxpayers. This is based on a stressed notional rate instead of the actual product rate, which is usually around 5.5% or the product rate plus 2%, whichever is higher (source: PRA and current BTL lender guidance, checked August 2026).

Let’s use our example home that rents for £1,400 a month as a test case. I will be a basic-rate taxpayer.

An amount of £262,500 plus 5.5% interest equals £14,437.50 a year, or £1,203 a month. At 125% ICR, the rent that is due is £1,203 × 1.25, which is £1,504 a month.

Our actual rent of £1,400 is less than the £1,504 that was asked for, so this loan amount would not pass a normal stress test at this rent level. If we work backward, the £1,400 a month in rent can actually support a loan of up to £244,000, which is about £18,500 less than the £262,500 we’re financing. In this case, the landlord would need either a bigger down payment to lower the loan amount or more rental income in order to qualify.

The interest-only payment at the real product rate is £262,525 times 5%, which comes to £1,094 a month, which can be easily covered by the £1,400 rent. The stressed assessment above, on the other hand, is what the lender actually tests against. The real numbers may show that a house is easily affordable, but the lender’s forward-looking stress test may still show that it is not.

A payment calculator only shows the mortgage payment. The real buy-to-let return relies on costs that aren’t shown in the calculator, like letting agent fees, ongoing upkeep, landlord insurance, and times when the property is empty between renters. The way landlord finance costs are taxed is also very different from other property ownership costs, and the rules have changed in the last few years. Instead of depending on this general summary, check with HMRC and a qualified accountant to see what the current rules are.

Commercial Mortgage Calculator UK

As there is no published rate table for commercial lending, the price is set case by case. Please use any number here as an example only. Commercial mortgages usually need a bigger down payment than domestic loans—often 30% or more—have shorter terms, and are based more on how well the business can pay back the loan with its own income than on a person’s income.

As an example, let’s say a business property costs £300,000 and you need to put down a 35% payment of £105,000. You would then pay back £195,000 over 15 years at a rate of 6.5%.

M = £195,000 × [0.005417 × (1.005417)²⁸⁰] ÷ [(1.005417)²⁸⁰ – 1] = about £1,699 a month

This number is just for reference; a real commercial mortgage quote will rely on the details of the business, its trading history, and the lender’s own risk assessment. You should talk to a commercial lender or broker to get an evaluation based on your business.

Mortgage Affordability Calculator UK

A mortgage payment calculator UK isn’t just a matter of multiplying your income by two. According to FCA rules (MCOB 11.6), lenders compare your monthly income to the amount you plan to spend. They then test the payment you would have to make at a higher interest rate to make sure you could still make it if rates went up. Standard high-street income multiples are usually between 4x and 4.5x gross annual income, but some lenders will offer 5x to 5.5x or even higher to certain borrower profiles. Stress margins are usually between 1 and 3 percentage points above the product or reversion rate (source: FCA MCOB 11.6 and current lender guidance, checked August 2026).

An example of this would be a family with a gross annual income of £70,000 (£5,833 a month) and £600 a month in fixed expenses. At a normal 4.5x multiple, that means the most that can be borrowed is about £315,000. This is before the lender does its own stress test and cost analysis to make sure that the payment is actually affordable.

The honest disclaimer that counts most in this case is that different lenders have very different multiples, stress margins, and ways of handling different types of income or existing obligations. This number is just a rough guess; it’s not a promise. A lender’s formal choice in principle, based on your actual income and expenses, is the only thing that gives you a real answer.

Mortgage Overpayment Calculator UK

When you make extra payments on your mortgage calculator UK, the amount of money you still owe goes down directly, which lowers all of your interest charges going forward. Adding £150 a month in extra payments to our example repayment debt would raise the payment from £1,535 to £1,685.

The loan is paid off in about 21 years instead of 25, which is about 4 years less time. The total amount of interest paid goes down from £197,940 to about £161,730, which is a savings of around £36,200.

It’s easy to miss this important UK-specific caveat: most mortgage rate calculator UK deals only let you make extra payments up to a certain percentage of the outstanding amount each year, usually around 10% a year, without being charged extra. If you pay more than the limit, you may be charged an early repayment charge (ERC), which is a fee based on a percentage of the amount you paid over the limit. This fee can significantly reduce or even cancel out the interest you were trying to save. Before making a lump sum or increased regular overpayment, you should always check your mortgage offer’s overpayment allowance. Do not assume that you can make as many overpayments as you want for free.

Costs Beyond the Monthly Payment

You have to pay more than just the mortgage to buy a home in the UK. For their better rates, lenders often charge product fees, which are sometimes called planning fees. These fees can be paid up front or added to the loan. The property’s value and the fees for the conveyancing solicitor are covered by the valuation and court costs.

The property transaction tax is a big tax that changes from country to country. Stamp Duty Land Tax (SDLT) is charged in England and Northern Ireland. There is a basic band with no rate and rising bands above it, plus an extra charge for properties that are bought after the first one. The Land and Buildings Transaction Tax (LBTT) is different in Scotland. There is a different band where the tax is not charged, and second homes are subject to an extra charge. Land Transaction Tax (LTT) is charged in Wales. It has its own different bands and no help for first-time buyers. These thresholds and rates are changed from time to time by HMRC, Revenue Scotland, and the Welsh Revenue Authority. For the most up-to-date information, check the current bands on GOV.UK or the site of the relevant devolved authority instead of relying on an old number.

Conclusion

A UK mortgage calculator isn’t just one number with a currency symbol attached to it. It’s a number of different products, each of which is evaluated differently, and if you get the wrong one applied to your case, you’ll get a wrong number. Before you assume that a generic calculator gave you a correct answer, run your own numbers through the right type above. Also, keep in mind that lender requirements are so different that only a formal decision in principle or advice from a qualified, FCA-regulated mortgage adviser can give you a clear number for your situation. You can get a reliable number by comparing each mortgage type on its own terms. This is true whether you’re comparing a standard repayment deal to an interest-only deal, a buy-to-let purchase to the rental income it generates, or just trying to figure out how much your fixed period will cost when it ends.

FAQs

Q1. How is a UK mortgage payment calculated?

M = P x [r(1+r)ⁿ] ÷ [(1+r)ⁿ − 1] is the usual formula for a repayment mortgage. For our example of £262,500 at 5% over 25 years, that’s around £1,535 a month. Interest-only, buy-to-let, and business mortgages employ a totally different computation as indicated above.

Q2. What happens when my fixed rate ends?

If you don’t switch to a new agreement, your mortgage will revert to the lender’s standard variable rate (SVR), which is usually higher than your fixed rate. In our example, the sum remaining after the 5-year fixed period was around £232,499, and that is what will be impacted by the new rate.

Q3. How is a buy-to-let mortgage assessed?

It is more based on the expected rental income of the property covering the mortgage interest by a required margin (an interest coverage ratio typically 125% to 145%) calculated at a stressed rate rather than the actual product rate, rather than personal income multiples as residential mortgages are done.

Q4. Can I overpay my mortgage without a penalty?

Usually yes, to a limit, usually approximately 10% of the outstanding debt a year on fixed-rate arrangements. Pay more than this and you could incur an early repayment charge. Always examine your unique mortgage offer before making any big overpayment.

Q5. How much can I borrow for a UK mortgage?

It is contingent upon your income, existing commitments, and the lender’s own stress test, often somewhere around 4x to 4.5x gross yearly income as a starting point, although there are differences from lender to lender and borrower profile to borrower profile. A formal decision in principle from a lender is just a definitive answer.

Q6. What’s the risk with an interest-only mortgage?

None of your payments go to capital. At the conclusion of the period, you still owe the whole loan total. And you’ll need a credible, distinct plan (a repayment vehicle) to clear that sum at the conclusion of the term, or you could be compelled to sell the property.