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ISA Allowance Optimiser (UK)

Plan how to use your remaining ISA allowance before the tax year ends.

See how much you'd need to invest each month to fully use your allowance - based on what you've already contributed.

No sign up. UK focused. Results are estimates only.

ISA Allowance Optimiser - Maximize Your £20,000 Annual Limit

Use this ISA Allowance Optimiser to see how efficiently you are using your £20,000 annual ISA allowance. Many savers underuse their allowance without realising the long-term impact on tax-free growth.

This tool estimates how much of your annual allowance is being utilised and highlights potential unused capacity over time. It is designed for UK investors who want to optimise contributions across cash or investment ISAs.

If you’re modelling long-term growth scenarios, explore the Advanced ISA Planner. For a full breakdown of ISA rules and limits, visit our ISA Guides.

ISA Allowance Optimiser

Months left in this tax year (1-12)

ISA allowance used this tax year (£)

Your ISA allowance plan for this tax year

£-

Allowance remaining

£-

Monthly needed

£-

Estimated ISA value after X years

Estimated ISA value after X years

What this calculation means

This optimiser shows how much you would need to invest each month, on average, to fully use your ISA allowance before the end of the current tax year.

You don't need to invest the same amount every month - this simply shows what's required on average.

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Want to see how contributions could grow over time?

ISA Plan provides educational calculators and planning tools. We do not provide financial advice.

Advanced planning

Advanced ISA Planner

For those who want a deeper view, the Advanced ISA Planner helps you explore longer-term scenarios, combine different ISA types, and model multiple tax years in one place.

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It's designed for users who want more flexibility and insight than a basic calculator can provide.

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  • Combine Cash and Stocks & Shares ISAs

  • Model multiple tax years and allowances

  • Adjust returns, contributions, and time horizons

  • Compare scenarios side by side

Free calculators remain avaliable. No subscription required to get started.

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How to use the ISA Allowance Optimiser​

  1. ​Enter how much ISA allowance you've already used this tax year

  2. Select how many months remain until the end of the tax year

  3. See the average monthly amount needed to use your remaining allowance

What people often do next

Review & adjust

Many users adjust the number of months or contribution pattern to see how different approaches could help them use their allowance.

Consider where to invest

After planning how much to contribute, some users look at investment platforms or savings accounts that support regular contributions and flexible deposits.

Plan longer term growth

Once your tax-year is clear, you can explore how these contributions might grow over time using the ISA Growth Calculator or Advanced Planner.

ISA Allowance Optimiser

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