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ISA vs SIPP calculator

ISA vs. SIPP Calculator: Which is Better for Your Savings?

Understanding the 2025/26 Tax Efficiency Battle

Both the Individual Savings Account (ISA) and the Self-Invested Personal Pension (SIPP) are powerful tax wrappers in the UK. However, they serve very different purposes depending on when you need your money and your current tax bracket.

Example presets

These presets show how the ISA vs SIPP trade-off can shift with tax rate and time horizon.

Compare an ISA and a SIPP

Use the same monthly budget in both options so the comparison stays fair and easy to understand.

What the result is saying

ISA pot

£157,190

You invest the same monthly budget directly from take-home pay.

Gross SIPP contribution each month

£375

The pension contribution after tax relief is added.

SIPP pot before retirement tax

£196,487

The full projected pension pot before withdrawals.

Estimated SIPP value after tax

£167,014

Assumes 25% tax free and the rest taxed at your chosen retirement rate.

That is about £9,824 more than the ISA on these assumptions.

Assumptions

  • The ISA is fully accessible, while the SIPP is normally locked until pension access age.
  • The SIPP assumes you can claim the full tax relief shown.
  • Investment returns, fees, and future tax rules can change.

Example scenario

Example scenario

This example shows a common ISA versus pension trade-off for someone investing each month.

  • Monthly budget: £300
  • Tax position: basic-rate taxpayer
  • Time horizon: 25 years
  • Assumed growth rate: 5% a year

A pension may start with a tax-relief boost, while an ISA keeps the money more accessible, so the best fit depends on flexibility as well as growth.

Learn the basics

How the ISA vs. SIPP Calculator: Which is Better for Your Savings? Works

Key Differences: Flexibility vs. Government Bonuses

Data updated for the 2025/26 UK tax year.

Both an ISA and a SIPP are tax-efficient UK wrappers, but they solve different problems. An ISA is built around flexibility because you can usually take money out whenever you want, while a pension is designed for retirement and normally stays locked away until later life.

A SIPP often wins on upfront tax efficiency. For a basic-rate taxpayer, an £80 contribution becomes £100 once tax relief is added, and higher-rate taxpayers may be able to claim back even more. That makes a pension powerful for long-term retirement saving.

An ISA usually wins on access. You do not get a government bonus when you pay in, but withdrawals are normally tax free and easy to reach, which can make an ISA better for medium-term goals or as a bridge before pension age.

Pros vs cons

Pros

  • Helps compare pension tax relief against ISA flexibility using the same monthly budget.
  • Useful for understanding the trade-off between accessible savings and locked retirement money.
  • Relevant for the 2025/26 UK tax year and common personal finance decisions.

Cons

  • Real outcomes can change if tax rules or pension access rules change later.
  • A SIPP can look stronger mathematically but may still be a poor fit if you need flexibility.
  • This is a simplified model and not a full retirement planning tool.

Glossary

ISA
An Individual Savings Account that lets UK savers and investors hold money in a tax-efficient wrapper.
SIPP
A Self-Invested Personal Pension that usually offers tax relief on contributions but keeps the money locked for retirement.

Frequently asked questions

Can I have both an ISA and a SIPP?+

Yes. Many people use a SIPP for retirement savings and an ISA for flexible money they may need before pension age.

What is the ISA limit for the 2025/26 tax year?+

The annual ISA allowance is £20,000. It does not roll over, so unused allowance is normally lost after the tax year ends on 5 April.

Which is better for a 40% taxpayer?+

A SIPP is often more attractive for a higher-rate taxpayer because the tax relief on the way in can be much stronger than the benefit of using an ISA alone.

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These calculators are for educational purposes only and do not constitute financial advice.

They use simplified assumptions and browser-based estimates. Read the full disclaimer before making important decisions.