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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.
Your ISA plan
£
£
%
20 years
Estimated balance after 20 years
£—
You invested£—
LISA government bonus£—
Investment growth£—
Lifetime ISA: the government adds 25% on contributions up to £4,000 per tax year (max £1,000/year). The £4,000 counts within your £20,000 ISA allowance.
The Lifetime ISA annual limit is £4,000 — your monthly plan exceeds this, so the government bonus is capped at £1,000/year.
Within the £20,000 ISA annual allowance for the 2026/27 tax year.
Contributions
Growth (incl. LISA bonus)
Show yearly breakdown
| Year | Contributions | LISA bonus | Growth | Balance |
|---|
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.
Open calculator →🌱
UK Savings Calculator
See how regular saving grows over time, in nominal pounds and adjusted for inflation.
Open calculator →Coming soon — UK Tax, Property & Retirement tools:
Income Tax · planned
Salary · planned
National Insurance · planned
Mortgage · planned
Mortgage Overpayment · planned
Stamp Duty · planned
Capital Gains Tax · planned
Dividend Tax · planned
Pension · planned
Retirement · planned
Compound Interest · planned
Investment Return · planned
UK Inflation · planned
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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.
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.