Mortgage Deposit Savings Calculator
Saving for a deposit is not simply a question of how much you can put aside each month — it is a race between your savings growing and the property price itself moving, since house prices rarely stand still while you save. This calculator works out how long reaching your target deposit would genuinely take, accounting for interest on your savings and, if selected, a Lifetime ISA bonus, while also showing what typical house price growth could do to the target itself along the way.
Saving for a Deposit
Work out how long to save your deposit and which LTV thresholds you can reach.
The Moving Target Nobody Warns You About
A deposit target based on today’s property price is not necessarily the target you will actually need to hit by the time you have saved enough, since the property price itself can rise during the saving period, particularly over a longer timeframe. This calculator applies a house price growth assumption across your projected saving period specifically to surface this effect, showing both what the deposit needs to be today and what the equivalent deposit could look like by the time you are projected to reach it. This is genuinely one of the most overlooked parts of deposit saving — treating the target as fixed when it is, in reality, a moving one.
This effect matters more the longer the saving period stretches out, since a modest annual growth rate compounds meaningfully over several years — a saving plan projected to take six or seven years faces a considerably larger moving-target effect than one projected to take just one or two, which is worth factoring into how realistic a very gradual saving pace actually is.
Why a LISA Can Cut Years Off the Timeline
A Lifetime ISA specifically accelerates deposit saving through its 25% government bonus on contributions up to £4,000 a year, which this calculator adds directly into your effective monthly saving rate when selected. This bonus is not investment growth or interest — it is added regardless of how your underlying savings perform, which makes it a genuinely reliable, guaranteed boost to the pace of saving rather than something dependent on market conditions or a specific interest rate holding steady.
Maximising the £4,000 annual LISA contribution before saving further into a standard account is generally the more efficient order to save in, since every pound within that annual limit attracts the guaranteed bonus, while additional saving beyond it does not — worth structuring monthly contributions with this priority order in mind rather than splitting evenly by default.
The Shortfall That Compounding Alone Can’t Close
If house price growth genuinely outpaces the combined effect of your monthly saving and any interest or bonus on top, this calculator will show a shortfall — a gap between what you are on track to have saved and what the actual target deposit will be by that point, given assumed house price growth. This is a sobering but useful thing to see clearly, since it highlights when simply continuing to save at the current rate will not be enough to keep pace, and when increasing the monthly contribution, extending the timeframe, or targeting a lower-priced property might genuinely be necessary to close the gap.
Seeing the Moving Target in Practice
Saving £400 a month with a Lifetime ISA bonus toward a 10% deposit on a £280,000 property, starting from £5,000 already saved, reaches the initial £28,000 target in roughly three years and eight months. But if house prices grow at 3.5% a year across that same period, the property itself is projected to reach roughly £317,600 by then, pushing the actual required 10% deposit to around £31,760 — leaving a shortfall of about £3,400 against the moving target, even though the original £28,000 goal was reached on schedule.
Picking a Realistic Target Percentage
The percentage deposit target you choose directly determines your future LTV, and therefore which mortgage rates you would likely access — a 5% deposit reaches the market at all but at the higher end of available rates, 10% improves the picture meaningfully, and 15% to 20% moves toward the more competitive rate bands. There is a genuine trade-off between saving longer for a larger deposit and better rate, versus getting onto the property ladder sooner with a smaller deposit at a less favourable rate — neither is universally correct, and this calculator lets you compare different target percentages directly against your own realistic saving rate. Our ISA Growth Calculator is useful for modelling the wider ISA landscape beyond just the Lifetime ISA bonus, and once a deposit target feels achievable, our Mortgage Affordability Calculator is the natural next step for working out how much you could realistically borrow alongside it.
Frequently Asked Questions
Should I use a Cash ISA or a Lifetime ISA for deposit saving?
A Lifetime ISA offers a 25% bonus specifically for a first home purchase or retirement, which a standard Cash ISA does not match, making it generally the stronger choice for deposit saving specifically, provided you meet the age and first-time buyer eligibility criteria.
What happens if house prices fall while I am saving?
This calculator assumes a positive growth rate by default, but entering a lower or even negative figure reflects a falling market instead, which would reduce or reverse the moving-target effect, making your saved deposit relatively more valuable against a falling target price.
Can family help contribute toward a deposit?
Yes — a gifted deposit from family is common and generally accepted by lenders, though it typically needs to be documented formally as a genuine gift, not a loan, as part of the mortgage application process.
Does a larger deposit always mean a meaningfully better rate?
Generally yes up to a point, though the improvement is not perfectly smooth — crossing a specific LTV threshold, such as from 85% to 80%, tends to unlock a more noticeable rate improvement than a similar-sized increase that stays within the same band.
Is it better to save in cash or invest for a deposit?
This depends heavily on your timeframe — a deposit needed within the next few years generally suits cash savings, given the lower risk of a market downturn just before you need the money, while a longer saving horizon may have room to consider investment growth, accepting the additional risk that comes with it.
Important Information
This calculator provides an estimate based on the assumptions you enter and does not constitute financial advice. Actual house price growth, savings rates and mortgage availability may differ from the assumptions used here. For advice specific to your circumstances, consult a qualified financial adviser. See our Disclaimer for further information.