Mortgage Deposit Calculator

What this calculator does

This deposit calculator turns a savings rate into a date. Enter the property price you are aiming at, the deposit percentage you want, how much you can put aside each month, and the mortgage rate you expect, and it returns the amount you need in pounds and how many months and years of saving it takes to get there.

The table beneath breaks it down year by year: what you have saved, what percentage of the property price that represents, and the monthly repayment you would face if you bought at that point. That last column is what turns an abstract savings goal into a decision about when to stop saving and start looking.

When to use it

Use it when you have a realistic price for the sort of property you want and need to know whether you are two years away or five. It is also the right tool for the LTV band question, which is peculiarly important in the UK — the table shows exactly when your saving crosses 10, 15, 20, and 25 percent of the price, and those are the moments your available rates improve.

Rerun it whenever your circumstances change: a pay rise, a partner joining the purchase, moving somewhere cheaper to save faster, or opening a Lifetime ISA. And use it to decide against waiting — if reaching the next band costs eighteen more months of rent, the table plus your rent figure will make the answer obvious.

Understanding the inputs

Property price should come from actual listings in the area you are searching, allowing for the fact that asking prices and sold prices differ. Target deposit is a percentage: five, ten, fifteen, twenty, and twenty-five percent are the values that map onto lenders' LTV bands, so those are the ones worth testing.

Monthly savings should be what you can sustain after rent and commitments, and should sit alongside — not instead of — an emergency fund. Do not plan to arrive at exchange with nothing left. The interest rate feeds the resulting repayment column; use a live product rate for the LTV band you expect to land in, since a 95 percent deal and a 75 percent deal are priced very differently.

How is this calculated?

Down Payment = Property Price × (Down Payment %) / 100. Months to Goal = (Down Payment − Current Savings) / Monthly Savings.

A worked example

Suppose you are aiming at a £280,000 home with a ten percent deposit and can save £900 a month. The target is £28,000 and the timeline is just under 32 months, so two years and eight months.

If you are a first-time buyer under 40, £4,000 of that annual saving can go into a Lifetime ISA and attract a £1,000 government bonus each tax year. Across three tax years that is £3,000 of free money, cutting roughly three months from the timeline. As a couple, both opening a LISA, the bonus doubles to £2,000 a year — closer to six months saved. On a £280,000 purchase, well under the £450,000 cap, it is the single highest-return thing a UK first-time buyer can do.

Limitations and assumptions

The calculator assumes no interest on savings, a fixed property price, and an uninterrupted savings rate — all optimistic or pessimistic in different directions. A rising market is the real risk, since your target grows while you save toward it.

It also excludes everything beyond the deposit: stamp duty, conveyancing, searches, survey, product fees, and removals, which together commonly add £5,000 to £12,000 in cash. It does not model Lifetime ISA bonuses, shared ownership, or gifted deposits, and it does not check that a lender would actually lend the balance — that depends on income multiples and affordability rather than deposit alone. Pair this with an affordability check and a quote for your upfront costs before setting a date.