How are monthly mortgage payments calculated?

Monthly payments are calculated using the standard amortisation formula, which accounts for compound interest. The formula takes your loan amount, annual interest rate, and term length to produce a fixed monthly payment that fully repays the loan by the end of the term.

What is a good LTV ratio?

Lower LTV ratios get better interest rates. Key thresholds: 60% LTV gets the best rates, 75% is very competitive, 80% is standard, 90% is higher risk with higher rates, and 95% is the maximum most lenders offer. Every 5% reduction in LTV can unlock a better rate.

Should I choose a 25 or 30 year mortgage?

A 25-year term has higher monthly payments but you pay significantly less interest overall. A 30-year term reduces monthly payments by around 10-15% but costs tens of thousands more in total interest. Choose based on what you can comfortably afford monthly while leaving room for rate rises.

How much interest will I pay over the full term?

On a typical £270,000 mortgage at 4.5% over 25 years, you'd pay around £180,000 in interest — roughly two-thirds of the original loan. This is why even small rate differences matter: 0.5% lower could save £15,000–£20,000 over the full term.

Mortgage Repayment Calculator

Calculate your monthly mortgage repayments, total interest paid, LTV ratio, and see how your balance reduces over time.

Property price

Deposit

Interest rate (%)

Mortgage term (years)

Monthly repayment

£1,501

LTV over 80% — expect higher rates; a bigger deposit helps.

Mainstream lenders price best at 60–80% LTV.

Total repayment

£450,224

Total interest

£180,224

LTV ratio

90.0%

Amortisation summary

Year	Balance	Equity paid	Interest paid
1	£264,019	£5,981	£12,028
5	£237,216	£32,784	£57,261
10	£196,178	£73,822	£106,268
25	£0	£270,000	£180,224

Based on a capital repayment mortgage with fixed rate throughout. Actual costs vary — most fixed rates are for 2–5 year periods.

Check what you can afford See full purchase costs Mortgage Overpayment Calculator

Estimates only, based on the assumptions you enter and current published rates. Not financial advice. Your actual costs depend on your circumstances and your lender. HomeThink is not authorised or regulated by the Financial Conduct Authority and recommends no lender or mortgage.

How mortgage repayments work

A capital repayment mortgage splits each monthly payment into two parts: interest on the outstanding balance, and repayment of the loan itself. In the early years, most of your payment goes toward interest. Over time, as the balance reduces, more goes toward paying off the principal.

The Loan-to-Value (LTV) ratio — your mortgage amount as a percentage of the property price — is one of the biggest factors in the interest rate you'll be offered. Dropping below key thresholds (90%, 80%, 75%, 60%) typically unlocks significantly better rates.

Most UK mortgages use a fixed rate for an initial period (typically 2 or 5 years), then revert to the lender's standard variable rate (SVR). It's important to remortgage before your fixed period ends to avoid a sudden payment increase.

Frequently asked questions

How are monthly mortgage payments calculated?: Monthly payments are calculated using the standard amortisation formula, which accounts for compound interest. The formula takes your loan amount, annual interest rate, and term length to produce a fixed monthly payment that fully repays the loan by the end of the term.
What is a good LTV ratio?: Lower LTV ratios get better interest rates. Key thresholds: 60% LTV gets the best rates, 75% is very competitive, 80% is standard, 90% is higher risk with higher rates, and 95% is the maximum most lenders offer. Every 5% reduction in LTV can unlock a better rate.
Should I choose a 25 or 30 year mortgage?: A 25-year term has higher monthly payments but you pay significantly less interest overall. A 30-year term reduces monthly payments by around 10-15% but costs tens of thousands more in total interest. Choose based on what you can comfortably afford monthly while leaving room for rate rises.
How much interest will I pay over the full term?: On a typical £270,000 mortgage at 4.5% over 25 years, you'd pay around £180,000 in interest — roughly two-thirds of the original loan. This is why even small rate differences matter: 0.5% lower could save £15,000–£20,000 over the full term.

Found a property?

Open a Rightmove, Zoopla or OnTheMarket listing with the free HomeThink browser extension for AI-powered analysis — red flags, neighbourhood data and the full monthly cost.

Get the free extension

Fixed rate, tracker, variable, and offset mortgages each carry different risks and costs. Here's how to choose the right mortgage type for your situation.

What Is a Mortgage in Principle and Do You Need One?

A mortgage in principle tells estate agents you can afford a property before you make an offer. Here's how to get one and what it doesn't guarantee.

Mortgage Protection Insurance: What It Is and Do You Need It?

When you have a mortgage, knowing which types of insurance cover you need — and which are optional — can save significant money.

Green Mortgages UK: Lower Rates for Energy-Efficient Homes

Green mortgages reward energy-efficient homes with lower rates. Find out which lenders offer them and whether a better EPC rating is worth chasing.

Got a specific property in mind?

Open any Rightmove, Zoopla or OnTheMarket listing with the free HomeThink browser extension and get a Free AI report with red flags, a score and neighbourhood intel in about a minute. Free account, no card required.

Get the free extension

More free tools

Affordability Calculator

Find out how much you can borrow and afford.

House Buying Costs Calculator

Estimate the total cost of buying a house in the UK.

Mortgage Overpayment Calculator

See how much interest and time you could save by overpaying your mortgage.