The race between deposits and interest
Every savings goal is a race with two runners, and one of them is usually barely jogging. The calculator advances month by month, compounding the balance at the twelfth root of the annual rate and then adding your deposit, until the balance crosses the target. But the date it produces matters less than the split it reports underneath: what you contributed and what interest added, as separate figures, because that ratio tells you which lever to pull. Over a two-year goal at 2%, interest typically supplies under 4% of the total; the deposit is doing essentially all the work. Stretch to a ten-year goal at 5% and interest can supply a quarter or more, at which point the rate you shop for starts to matter.
Unlike the retirement tools on this site, this is deliberately a nominal calculation. A goal two or three years out is a real price (a deposit, a car, a wedding), and a headline savings rate is the honest number to plan against. As for which rate to enter: whatever a real account pays you today, not the best rate in a comparison table you have not opened, and if unsure, assume slightly less, since an early finish is a nicer surprise than a late one. Do not count on it holding either. Easy-access rates move with the base rate, and introductory bonuses expire, often after twelve months.
Maya's month 26
Maya wants £12,000 for a house deposit. She starts with £2,600 and can save £340 a month into an account paying 4.1%. She reaches the target in month 26, two years and two months, and of the roughly £12,060 sitting there at the crossing, £2,600 was her starting balance, £8,840 came from 26 monthly deposits, and about £620 came from interest.
Change a single input and the levers show their relative strength. Raising the deposit to £400 a month brings the target to month 23, three months earlier. Finding a 5.1% account instead still lands in month 26: a full extra percentage point of interest does not move the date by a single month. Pushing the target up to £15,000 lands at month 34, eight months later. That is the honest shape of a short goal: on a two-year horizon the monthly amount does nearly all the work, so shopping for rate is fine, but it will never rescue a plan the monthly amount cannot support.
Any lump sum you already hold should go in immediately, because it earns from day one; the monthly figure is for money you have not earned yet. Where the money should live depends on the deadline. For under a year, easy access. For a fixed date beyond a year, a fixed-rate bond usually pays more, provided you can genuinely lock it away. The goal guide takes both questions further, including what to do when the monthly number comes back too big to live with.
What the date quietly assumes
The projection believes your contributions arrive unbroken, and one missed month pushes everything back, which is precisely why the 52-week challenge exists as a structured alternative. It credits interest monthly, while real accounts vary: some pay annually, some on an anniversary date, and annual crediting earns fractionally less than the monthly compounding shown, though at these rates and timescales the difference is a few pounds rather than anything that changes a decision. Tax on interest is not deducted either. Above the personal savings allowance, part of that interest goes to HMRC, so treat the interest figure as a ceiling.
Inflation is not applied, and for goals beyond three or four years the thing you are saving for is likely getting more expensive too; the inflation calculator shows the erosion. That timescale is also where this tool stops being the right one at all. It is not for investing: money you might need within five years does not belong in markets, and for anything longer, use the FIRE calculator rather than a savings account projection.
One boundary confuses people more than any other, so it deserves its own line. A goal has a target and an end date; an emergency fund is a permanent buffer sized from your monthly essentials, and the emergency fund calculator handles the second.