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Simple Financial Calculators for the UK

Free tools to help you understand savings, ISAs and investments — with transparent maths and up-to-date UK rules.

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Tool
£—

Your ISA plan

£
£
%

Presets are illustrative. Adjust the rate to match your own assumption.

20 years
Estimated balance after 20 years Growth share —
£—
You invested£—
Investment growth£—
Within the £20,000 ISA annual allowance for the 2026/27 tax year.
Contributions Growth (incl. LISA bonus)
Show yearly breakdown
YearContributionsGrowthBalance

Popular calculators

Every tool is instant, transparent about its maths, and shares with one link.

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ISA Calculator

Model a Cash, Stocks & Shares or Lifetime ISA — including the 25% LISA bonus and your £20,000 annual allowance.

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UK Savings Calculator

See how regular saving grows over time, in nominal pounds and adjusted for inflation.

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Compound Interest Calculator

See how compounding frequency — daily to annually — and regular contributions grow your money.

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Investment Return Calculator

Model investment growth, or work out the monthly amount you need to reach a target.

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UK Income Tax Calculator

See your 2026/27 Income Tax by band, your Personal Allowance and effective rate.

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UK Salary Calculator

Work out take-home pay after Income Tax and National Insurance — monthly and weekly.

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National Insurance Calculator

See your Class 1 employee National Insurance by band — 8% and 2% — for 2026/27.

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UK Mortgage Calculator

Work out monthly repayments, total interest and LTV — repayment or interest-only.

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Mortgage Overpayment Calculator

See how much interest you save and how much sooner you clear your mortgage with a monthly overpayment.

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UK Stamp Duty Calculator

Estimate Stamp Duty in England & NI, Scotland and Wales for 2026/27 — with first-time buyer relief.

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UK Pension Calculator

See how your pot, contributions, tax relief and growth add up by retirement — and your 25% tax-free lump sum.

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UK Retirement Calculator

Find the income gap, the pot you need and the monthly saving to get there — State Pension included.

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UK Capital Gains Tax Calculator

Estimate CGT for 2026/27 — chargeable gain, the £3,000 allowance, and 18%/24% rates.

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UK Dividend Tax Calculator

See what you owe on dividend income after the £500 allowance at 2026/27 rates.

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UK Inflation Calculator

See what money is worth over time with CPI inflation — and the buying power you lose.

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Transparent maths

Every calculator shows its formula and assumptions. No black boxes.

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No sign-up

Open the page and calculate. No accounts, no email walls.

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No data stored

Everything runs in your browser. Your numbers never leave your device.

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UK rules

Thresholds reference official GOV.UK sources and state the tax year they apply to.

Built for UK rules. Checked against official sources. Calculated in your browser — How we calculate →

Frequently asked questions

Is Casvia free?
Yes. All calculators are free, require no sign-up and store no data. Everything is computed locally in your browser.
Do you collect or sell my data?
No. Casvia has no tracking scripts, no analytics and no server. The numbers you enter never leave your device. See our Privacy policy.
Why does the ISA calculator mention a tax year?
UK ISA rules are set per tax year (6 April – 5 April). The calculator uses the 2026/27 allowance of £20,000 and flags upcoming changes, so the figures stay current.
Are these results financial advice?
No. These are educational tools. Returns are hypothetical and assume a constant rate — they do not include fees, taxes on non-ISA accounts, or market volatility. See our Disclaimer.
What return rate should I use?
It depends on the ISA. Cash ISAs currently pay interest in the low single digits; Stocks & Shares ISAs have historically returned more over the long term but come with risk. Try 4%, 5% and 7% presets to compare.