Both are tax-advantaged. Both have £20k/£60k annual limits. But they work very differently.
Pension wins on tax efficiency at the margin
Basic-rate taxpayer? Your £80 becomes £100 inside the pension (20% relief). Higher-rate (40%)? Your £60 becomes £100. Additional-rate (45%)? £55 becomes £100.
If you'll be a basic-rate taxpayer in retirement, pension beats ISA by roughly the additional tax relief at today's bracket minus basic relief at retirement. For a higher-rate earner, that's 20% — massive.
ISA wins on flexibility
Pensions lock your money until 55 (rising to 57 from 2028). ISAs: withdraw anytime, no penalty, no tax. If you might need the money before age 55, ISA is the only answer.
The right answer for most people
Ordinary rule: Contribute to pension at least up to any employer match (free money). Then max your ISA. Only if both are exhausted, add more to pension.
High-earner tweak: Above £100k income (where sipp-vs-sipp" data-autolink="glossary">personal allowance tapers), pension contributions are uniquely valuable. A £1,000 pension contribution can save 60% tax (40% plus restoration of personal allowance). Max pension first here.
The numbers
Use our ISA Calculator and Pension Calculator to compare scenarios with your own inputs.