UK Mortgage Calculator
Plan smarter. See your monthly payment, total cost and affordability in seconds.
Your Mortgage Details
See your mortgage results
Enter your details on the left, then press Calculate to reveal your full breakdown.
Explore More Property Tools
Everything a first-time buyer actually needs to understand
A mortgage is the biggest number most of us will ever sign for — yet the way it works is rarely explained clearly. This guide walks through it visually, one idea at a time: how your payment is built, why the timing of an overpayment matters so much, how your deposit changes the rate you’re offered, and the real costs that sit alongside it. No jargon, no assumed knowledge. All examples use a £270,000 loan at 4.5% over 25 years unless noted.
How a repayment mortgage is actually built
Every month you pay the same fixed amount. But that single payment is quietly doing two different jobs at once. Part of it is interest— the lender’s charge for letting you borrow the money. The rest is capital— the bit that actually reduces what you owe. Interest is always calculated on the balance that’s still outstanding, so in the early years — when the balance is huge — most of your payment is interest. As the balance shrinks, the interest shrinks with it, and more of the same payment goes to clearing capital. The mix flips slowly, year after year.
This is why a mortgage feels slow to move at first. In year one, only around a fifth of what you pay is chipping away at the debt. By the final years, almost all of it is. Nothing about your payment changes — only the invisible split inside it.
What £1 of your payment really buys
Zoom into a single pound of a single payment and the story becomes obvious. Early on, most of that pound vanishes as interest. Somewhere near the middle of the term, the balance tips and the pound starts pulling its weight against the debt. By the end, nearly the whole pound is capital.
Understanding this one picture explains almost every smart mortgage decision: shortening the term, overpaying, or remortgaging all work by attacking the balance sooner, so less of your money is lost to interest along the way.
Why overpaying early saves so much more
Because interest is charged on the outstanding balance, a pound of capital removed in year one avoids interest for the next twenty-four years. The same pound removed in year twenty avoids almost nothing. Overpayments are a compounding force, and time is what makes them powerful — which is why a modest, steady overpayment early beats a large one later.
Most UK lenders let you overpay up to 10% of the balance each yearwith no early-repayment charge. Even rounding your payment up by £50 or £100 quietly rewrites the second half of your mortgage. Always check your lender’s specific overpayment limit first — the calculator above lets you model any amount.
The LTV ladder — and why crossing a rung matters
Loan-to-value (LTV) is simply your loan divided by the property price. Borrow £270,000 on a £300,000home and you’re at 90% LTV. Lenders price risk in bands, and the rate they offer improves sharply each time you drop under a threshold — typically at 90%, 85%, 80%, 75% and 60%. Nudging your deposit just over one of these rungs can cut your interest rate for the entire deal, which is often worth far more than the extra deposit itself.
A worked example: lifting your deposit on that £300,000 home from £30,000 (90% LTV) to £45,000 (85% LTV) might drop your rate by around 0.3–0.5%. On a £255,000 loan that’s roughly £50–£80 a month, every month, for the length of the fix — many times the £15,000of extra deposit over the years. If you’re close to a band, it’s almost always worth stretching for it.
Fixed rates, and the reversion cliff
The headline rate you’re quoted almost never lasts the whole term. Most UK mortgages are fixed for 2, 5 or 10 years, and when that fix ends the loan reverts to the lender’s Standard Variable Rate (SVR)— usually several percentage points higher. That’s the moment to remortgage onto a new deal.
This is also why lenders stress-testyou: before they lend, they check you could still afford the payment if rates rose by two or three percent. Budget the same way. The “If rates move” panel in the calculator shows exactly what a 1% or 2% rise would add to your monthly payment — treat that higher figure as your real ceiling.
Repayment vs interest-only, side by side
Almost every residential mortgage today is repayment: your payments clear the whole loan by the end of the term. Interest-onlykeeps monthly payments much lower because you only pay the interest — but you still owe the entire loan at the end and need a separate plan (savings, investments, or selling) to clear it. It’s now mostly a buy-to-let product.
The true upfront cost, beyond the deposit
Your deposit is the big number, but it isn’t the only one due on completion. On a typical £300,000purchase, plan for a few thousand pounds of extras on top — get these wrong and a deal that looked affordable suddenly isn’t.
Stamp Duty is usually the largest, and it depends on price and whether you’re a first-time buyer — use our Stamp Duty calculator for the exact figure. Legal (conveyancing) fees, a survey, the lender’s product/arrangement fee and removals fill in the rest. A sensible rule of thumb is to keep a cushion of £3,000–£8,000 beyond your deposit.
The seven terms worth knowing
Frequently asked
Should I overpay or invest instead?+
Rule of thumb: if your mortgage rate beats the after-tax return you'd realistically get elsewhere, overpay. At 4–5% mortgage rates, overpaying is often the guaranteed, tax-free win. Check your lender's limit first — usually 10% of the balance a year before any early-repayment charge.
Is interest-only actually cheaper?+
Each month, yes — you only pay interest, so payments are much lower. But you still owe the entire loan at the end and need a repayment vehicle (investments, ISA, or selling) to clear it. UK lenders rarely offer interest-only for residential mortgages now; it's mostly a buy-to-let product.
Why does overpaying early save so much more?+
Interest is charged on the outstanding balance, so early in the term almost all of your payment is interest. Overpaying then removes capital that would otherwise accrue interest for decades. The same overpayment in year 20 barely moves the needle — timing is everything.
What is LTV and why do the bands matter?+
Loan-to-value is your loan divided by the property price. Lenders price risk in bands — you typically unlock better rates at 90%, 85%, 80%, 75% and 60% LTV. Nudging your deposit over one of these thresholds can cut your rate for the whole deal.
Is the headline rate what I'll pay for the whole term?+
Almost never. Most UK mortgages fix for 2, 5 or 10 years, then revert to the lender's Standard Variable Rate — often several points higher. Plan to remortgage at the end of your fix, and stress-test your budget against a higher rate.
Keep exploring
Every figure here is an estimate. The exact amount your lender quotes depends on their product fees, any cashback and how interest is calculated (daily vs monthly). Always check the official Key Facts Illustration before you commit.