Hundred SummersHouse deposit calculator: how long to save, and what the Lifetime ISA does to it
Your monthly saving compounded at your rate against the deposit you need, with and without the Lifetime ISA’s 25% bonus, and the LISA rules (age, price cap, first-time buyer) applied before the bonus is counted. Your figures never leave your browser.
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Worked example
Computed when this page was built by the same engine that runs the calculator above, so the figures below and the live tool can never disagree. Change any input above to see your own.
| Inputs | |
|---|---|
| Target home | £300,000 |
| Deposit | 10% = £30,000 |
| Saved so far | £6,000 |
| Saving a month | £500 |
| Interest rate | 4.0% |
| Age / Lifetime ISA | 28 / yes |
| Results | |
|---|---|
| Without a Lifetime ISA | 3 years 8 months |
| With the Lifetime ISA bonus | 3 years 2 months |
| Bonus received along the way | £3,250 |
| Months saved | 6 |
The next question
How much could I borrow? →Mortgage affordability calculator
Or answer it with everything else: the full Hundred Summers plan connects your pay, pensions, savings, property, tax and spending year by year, and stress-tests them across 500 simulated market histories.
Read the guide
- Stamp duty when you move: three taxes and the buy-before-you-sell surcharge →SDLT, LBTT and LTT side by side at 2026/27 rates, worked figures for a £300,000 home in each nation, why the additional-property surcharge catches ordinary movers, and the refund window if the old home sells later.
The bonus, and its small print
The Lifetime ISA is the only account that adds 25% to a first-time buyer’s savings, and for anyone under 40 saving for a home under £450,000 it is close to free money: £4,000 in, £5,000 out, every year. The rules bite in three places. It must be opened before 40 and held 12 months before use; the home must cost £450,000 or less (a hard cap, with no relief above it); and money withdrawn for anything else before 60 loses 6.25% of your own savings, so a LISA is a commitment to buying, not a general savings account.
After the deposit
The deposit decides the price range through the loan-to-value cap, and the mortgage affordability calculator shows what income then supports. Budget the other costs of buying: stamp duty (nothing for first-time buyers to £300,000 in England), legal fees, survey and moving. The Lifetime ISA calculator follows the account through to 60 for anyone who ends up not using it for a home.
Sources
- HMRC, Lifetime ISA (bonus, limits, age, price cap, withdrawal charge).
- Stamp duty for first-time buyers: HMRC SDLT residential rates.