ISA Allowance Calculator
Use this isa allowance calculator to test a UK scenario. Enter your own figures, review the formula trace and compare the result with the official source before making a material decision.
Quick answer
ISA Allowance Calculator provides a transparent UK planning estimate using the inputs shown, a visible formula trace and a versioned 2026/27 method. Check every statutory rate or threshold against the linked official source. The result is educational and is not an official assessment, provider quote or personalised advice.
Calculator
How to use this calculator
- Enter figures for one clearly defined scenario.
- Check the effective date, jurisdiction and official source.
- Review the formula trace and test a second scenario before acting.
Explanation
What it is
ISA Allowance Calculator provides a transparent UK planning estimate using the inputs shown, a visible formula trace and a versioned 2026/27 method. Check every statutory rate or threshold against the linked official source. The result is educational and is not an official assessment, provider quote or personalised advice.
How it works
Tapering, carry forward and special definitions must be checked separately.
When to use it
Use it to compare scenarios, prepare questions and understand the effect of each input before checking the official assessment or provider terms.
Limitations
- The result is an estimate based only on the displayed inputs.
- Rates, thresholds and provider terms may change after the effective date.
- The tool does not replace an official calculation, regulated advice or a personalised offer.
Key terms
- Estimate
- A result produced from the displayed inputs and assumptions, not a guaranteed outcome.
- Effective date
- The date or tax year for which a changing rule or rate has been checked.
- Formula trace
- The visible sequence showing how inputs become the result.
Formula
How we calculate this
Tapering, carry forward and special definitions must be checked separately.
Statutory or methodological reference:GOV.UK official guidance — Individual Savings Accounts.
Formula trace: Compound-growth or retirement-income model with contribution timing, fees, inflation, tax wrapper/allowance and rate-change assumptions; show nominal and real outcomes.
Worked example
Place £5,000 into a scenario earning an illustrative 4% a year for three years, with interest compounded monthly where the page uses a growth model. The rate is an input, not a live product rate. Check the governing rule at GOV.UK official guidance — Individual Savings Accounts.
FAQ
What does the isa allowance calculator calculate?
Tapering, carry forward and special definitions must be checked separately.
Which source should I check?
Use the linked GOV.UK official guidance — Individual Savings Accounts page and confirm that its effective date matches your scenario.
Is the result an official assessment?
No. It is an educational estimate and may omit facts used by an authority, adviser or provider.
Why can my real result differ?
Pay-period rules, tax codes, household facts, reliefs, fees, provider criteria and later policy changes can alter the result.
When should I recalculate?
Recalculate after any change in income, balance, rate, term, tax year, household facts or official policy.
Common mistakes
- Mixing monthly and annual inputs.
- Using an old or promotional rate without checking its date and conditions.
- Treating an estimate as a binding decision or guaranteed product outcome.
Tips
- Save the inputs and effective date.
- Change one assumption at a time.
- Compare the result with the specific official source before acting.
Related calculators
Related guides
Sources and editorial review
- GOV.UK official guidance — Individual Savings Accounts
- GOV.UK official guidance — How Isas Work
- Financial Conduct Authority guidance — Investsmart
Author and review
Author: FinanceHub UK Editorial Team — Editorial. Editorial policy.
Reviewed by role: Investment specialist and FCA compliance reviewer. Named qualified reviewer sign-off is pending before production.
Review record date: 2026-07-10. Next review due: 2027-03-01.