Savings Growth Calculator.
Compound interest on regular saving — what patience is actually worth in pounds.
Compound growth with monthly contributions, interest compounded monthly. The split between what you put in and what the interest added is the part worth staring at — it is the whole argument for starting early. Interest outside an ISA may be taxable once past your savings allowance — Everything runs in your browser — your figures never leave it. Estimates are general information, not advice: ask us about your own position.
Patience, priced
What the eighth wonder actually pays.
Compound interest is easy to praise and hard to feel — until you see the split this calculator shows: how much of the final balance you contributed, and how much the interest added on its own. Run twenty years of steady saving and the interest line quietly overtakes the contributions line; that crossover is the entire argument for starting early, made in pounds rather than proverbs. The mechanics here are straightforward: monthly compounding at a steady rate on a starting sum plus regular monthly additions.
The tax footnote most savers meet eventually: outside an ISA, interest above your Personal Savings Allowance (£1,000 for basic-rate taxpayers, £500 for higher-rate, nil for additional-rate) is taxable — and at today's rates a solid cash balance crosses that line faster than people expect. For business owners there is a second question with bigger numbers attached: surplus cash sitting in the company has its own options — and consequences for reliefs — that deserve proper advice rather than habit.
Common questions.
Is interest on savings taxable?
Above your Personal Savings Allowance, yes — £1,000 a year tax-free for basic-rate taxpayers, £500 for higher-rate, nothing for additional-rate. ISA interest is always tax-free and doesn't touch the allowance. HMRC usually collects the tax via your tax code or Self Assessment from bank-reported data.
What rate should I assume?
For cash, today's achievable easy-access or fixed rate — not the headline bonus rate that expires in three months. For long-horizon projections, be conservative: a rate that flatters the projection only postpones the disappointment. Run two rates and treat the gap as your uncertainty.
My company has surplus cash — same maths?
The compounding is the same; everything around it differs. Corporate interest is taxable in the company, and a large investment cash pile can affect reliefs like Business Property Relief and even trading-company status for CGT purposes. Deliberate choices — corporate savings, pensions, dividends, investment — beat leaving it in the current account by default.
Keep going.
Tax Reserve Calculator
The first thing to save for is January — put the tax aside before the dreams.
Open →Inheritance Tax Estimator
Long-term saving eventually meets the frozen bands — see when.
Open →Tax advisory
Company cash, pensions and ISAs in one plan instead of three habits.
Open →Prefer a human with the numbers?
Saving hard is the easy half — where the money sits decides what the taxman takes of the growth. Worth one conversation.