ToolWren"How much is a £300,000 mortgage a month?" It is one of the most-searched money questions — and the answer depends on just three things beyond the price: your deposit, the interest rate and the term. Here is how the maths works and how to bring the payment down.
The four numbers that decide your payment
Every mortgage payment comes from: the property price, your deposit (which is subtracted to give the amount you borrow), the interest rate, and the term in years. Change any one and the monthly figure moves. The quickest way to see it is to plug them into our mortgage calculator — it shows the monthly payment, total interest and payoff date instantly.
How the monthly payment is calculated
Mortgages are amortised: you pay the same amount each month, but early payments are mostly interest and later ones mostly capital. The formula is M = P × r × (1+r)ᴺ ÷ ((1+r)ᴺ − 1), where P is the loan, r is the monthly rate (annual ÷ 12) and N is the number of months (years × 12). For example, £200,000 borrowed at 6% over 30 years works out to about £1,199 a month — and around £231,000 in interest on top of the £200,000 borrowed.
Why your deposit matters so much
Your deposit reduces the amount you borrow pound for pound, so it lowers both the monthly payment and the total interest. It also affects the rate you are offered — bigger deposits usually unlock cheaper deals. Most lenders want somewhere between 5% and 20%; enter a percentage in the calculator and it shows the cash figure, so you can see exactly what moving from a 10% to a 15% deposit does to your payment.
Term: the trade-off nobody explains
A longer term lowers your monthly payment — but you pay interest for longer, so the total cost rises, often by a lot. A shorter term costs more each month but far less overall. There is no single right answer; it is a trade-off between monthly affordability and lifetime cost, which is exactly why seeing both figures side by side helps.
Don't forget the extras
The headline payment is only principal and interest. Your real monthly cost usually also includes property tax and home insurance, and sometimes mortgage insurance or service charges — add these in the calculator's optional section for a true figure. Before committing, sanity-check the borrowing against your income with the salary calculator, and see how saving instead would grow with the compound interest calculator. This is general information, not financial advice.