The method
How it is worked out
Left = annual limit − paid in; benefit = contribution × ((1 + g)^n − (1 + g × (1 − tax))^n)
- g
- Expected growth
- tax
- Rate that would apply to growth outside the wrapper
Tax-Free Allowance Calculator
See how much of this year's ISA, 401(k), TFSA or Super allowance you have left and what filling it is worth over time. The result updates as you type so you can compare scenarios quickly.
Keep in mind
What it leaves out
- Rules differPension and Super access is restricted; ISA and TFSA are not.
- Carry-forwardSome allowances (pension, RRSP) carry forward; ISA and TFSA-style limits shown here do not.
- Contribution limitsLimits are held in an editable table for the current year.
Use the calculator to compare scenarios rather than as a guaranteed forecast.
About the Tax-Free Allowance Calculator
See how much of this year's ISA, 401(k), TFSA or Super allowance you have left, how much you can still add before the deadline, and what sheltering that money from tax is worth over the years ahead.
How it works and an example to tryShow less
How to use the result
Remaining allowance is the annual limit for your country less what you have paid in. The amount you can still add is the lower of that and your monthly amount times the months left. The benefit is the difference between growth untaxed and growth taxed at your rate, compounded over the years entered.
Example to try
With £6,000 of a £20,000 ISA limit used and six months left at £500 a month, you can add £3,000 and leave £11,000 unused. Sheltering the £3,000 from 20% tax on 6% growth is worth about £1,700 over 20 years.
Put it to work
Try it on a real situation
Load an example
What moves the result most
Worked out from your figures above. Tap a row to try it.
Who uses it, and when
Savers and investors near the end of a tax year, people starting to invest and anyone deciding between a wrapper and a general account.
Mistakes worth avoiding
- Assuming the allowance carries over when it does not.
- Leaving contributions to the last week and missing the deadline.
- Filling the wrapper with cash that needs to be accessible next month.
Questions
What does the Tax-Free Allowance Calculator do?
See how much of this year's ISA, 401(k), TFSA or Super allowance you have left and what filling it is worth over time.
How should I use the result?
Remaining allowance is the annual limit for your country less what you have paid in. The amount you can still add is the lower of that and your monthly amount times the months left. The benefit is the difference between growth untaxed and growth taxed at your rate, compounded over the years entered.
Does TechBullion store the information I enter?
The core calculation or transformation runs in your browser. Normal website security and analytics may still record page-level events, but the tool does not need to create a public record from your inputs.
What mistakes do people make with a tax-free allowance calculator?
Assuming the allowance carries over when it does not. Leaving contributions to the last week and missing the deadline. Filling the wrapper with cash that needs to be accessible next month.
Is the result guaranteed?
No. Use the result as a practical check or planning aid and verify important decisions with the relevant primary source, provider or professional advice.
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Results are estimates based on the figures entered, for general information only, and not financial, investment, tax or legal advice. See our terms of use.