Savings Calculator

Use the savings calculator above

Enter your current balance, the amount you plan to add each month, the interest rate the account pays and how long you want to save for. The tool projects your final balance and splits the result into the money you paid in versus the interest you earned, so you can see exactly how much of the growth came from saving and how much came from the interest itself.

How savings interest grows

Interest is the reward the bank or building society pays you for keeping your money with them. The rate is quoted as an annual figure, usually shown as the AER (Annual Equivalent Rate), which lets you compare accounts on a like-for-like basis no matter how often they pay out.

The real power comes from compounding. When interest is added to your balance, the next round of interest is calculated on the larger amount, so you start earning interest on your interest. Over a year or two the effect is modest. Over ten or twenty years it becomes the main driver of your final balance.

The plain-English formula for a one-off lump sum is:

Final balance = Starting amount × (1 + interest rate) raised to the number of years

So a rate of 4% means multiplying by 1.04 once for every year your money stays put. If you also pay in monthly, each deposit earns interest from the month it lands until the end of the term, so earlier payments grow more than later ones. The calculator above does this month by month, which is why its figure is more precise than a quick back-of-the-envelope sum.

Two things change the outcome more than people expect: how often interest is compounded (monthly compounding beats annual at the same headline rate) and whether interest is left in the account to keep growing or paid away into a current account. If you withdraw the interest, you lose the compounding and the maths reverts to simple interest. If you want to dig deeper into the compounding mechanics on their own, our compound interest calculator walks through the formula step by step.

Lump sum versus saving monthly

Most people fall into one of three camps: a single lump sum they want to grow, a steady amount they can set aside each month, or a mix of both. This savings calculator handles all three, and the difference between them is worth understanding.

A lump sum left untouched gets the full benefit of compounding from day one, because the whole amount is working from the start. Regular monthly saving builds the habit and suits most household budgets, but each pound has less time in the account, so the interest portion grows more slowly at first and accelerates later. Combine the two and you get the best of both: an upfront base that compounds plus fresh deposits topping it up.

If your plan is specifically a monthly regular saver with a fixed term and a capped deposit, the projection works slightly differently, and our regular savings calculator is tailored to that. For a goal-first approach, where you know the target and want to work backwards to the monthly amount, try the savings goal calculator instead.

How the savings calculator works

The tool runs your figures month by month. Each month it takes your running balance, adds your monthly deposit, then applies one twelfth of the annual rate as interest before carrying the new total into the next month. Repeating that for the full term gives a far more accurate result than applying a single annual rate once, especially when you are paying in regularly.

At the end it shows three numbers that matter: your final balance, the total you actually paid in (starting amount plus all your deposits), and the interest earned, which is simply the final balance minus what you put in. Seeing those three side by side is the quickest way to judge whether a rate and a time period are worth committing to.

Because savings rates are set by individual banks and move with the market, there is no official fixed figure to plug in. Use the rate your chosen account actually advertises. The Bank of England base rate influences savings rates but is not the rate you earn, so always check the account's own AER.

Worked example: Priya's three-year plan

Priya has £5,000 sitting in a current account earning almost nothing. She opens an easy-access savings account paying 4% AER, moves the £5,000 across, and decides to add £200 every month for three years. Here is how her balance builds, rounded to the nearest pound.

After three years Priya has paid in £12,200 of her own money and earned roughly £1,070 in interest, for a balance of about £13,270. The interest is small in year one because the deposits have not had long to compound, then it climbs steadily as the balance grows. Leave the same plan running for ten years at the same rate and the interest portion becomes the largest single contributor to the pot, which is the whole point of starting early and leaving it alone.

Do you pay tax on savings interest?

For most people the answer is no, thanks to the Personal Savings Allowance (PSA). This lets a basic-rate taxpayer earn up to £1,000 of savings interest a year tax-free. A higher-rate taxpayer gets £500, and additional-rate taxpayers get £0. Interest above your allowance is taxed at your normal income tax rate.

There is also a starting rate for savings of up to £5,000 at 0%, aimed at people with low non-savings income; it tapers away as your other income rises, so it mainly helps those with modest earnings or pensions. And anything held inside an ISA is completely tax-free regardless of how much interest it earns, which is why an ISA is worth considering once your interest starts approaching your allowance.

These allowances are UK-wide. Scotland sets its own income tax rates, but the Personal Savings Allowance and the tax treatment of savings interest are the same across England, Wales, Scotland and Northern Ireland, so you do not need a separate calculation depending on where you live. For the official guidance on saving sensibly, see MoneyHelper's how to save guide.

Source: gov.uk – tax on savings interest, checked for the 2026/27 tax year.

How to make your savings work harder

The calculator shows the maths, but a few practical moves change the result more than chasing an extra fraction of a percent on the rate.

• Use your ISA allowance first. If your interest is heading towards your Personal Savings Allowance, a cash ISA keeps the growth tax-free and out of any future allowance squeeze.
• Watch for bonus rates that drop off. Many easy-access accounts pay a headline rate for 12 months, then fall. Set a reminder to move your money when the bonus ends, or your projection quietly stops matching reality.
• Keep emergency money accessible. Locking everything into a fixed-rate bond for a better rate is fine, but only with money you genuinely will not need before the term ends.
• Pay in early in the month. Deposits made earlier earn interest sooner. Over years this nudges your final balance up at no extra cost.
• Re-run the projection when rates change. A savings rate is not fixed for life. When the market moves, update the rate in the calculator to see the real picture.

Common mistakes to avoid

A savings projection is only as good as the assumptions behind it, and a few errors crop up again and again.

• Treating the headline rate as guaranteed. Easy-access rates are variable and can change at short notice. The number you see today is not promised for the whole term.
• Forgetting tax on large balances. Once your interest passes your Personal Savings Allowance, the excess is taxed, which quietly reduces your real return. HMRC usually collects this through your tax code or self assessment rather than the bank.
• Confusing AER with the gross rate. AER includes the effect of compounding within the year; the gross rate does not. Compare accounts on AER to be sure you are comparing like with like.
• Ignoring inflation. A balance can grow in pounds while losing buying power if inflation outpaces your rate. The calculator shows nominal growth, not what it will buy.
• Assuming the rate compounds when interest is withdrawn. If you spend the interest each month rather than leaving it in, you get simple interest, not compound, and the long-term figure is lower.

These estimates are for general guidance only and are not personal financial or tax advice. Your actual return depends on your account's terms, future rate changes and your own tax position.

Related calculators

Once you have a projection, these tools help with the next decision. The compound interest calculator breaks down the growth formula in detail, the regular savings calculator is built for monthly regular savers, and the interest calculator works out simple and compound interest on any amount. To plan around a target figure, use the savings goal calculator.

Related tools

• Savings interest tax calculator, check if you owe tax on your interest.