Cash ISA vs Stocks & Shares ISA Calculator 2026/27

Project the same contributions across a Cash ISA and a Stocks & Shares ISA side-by-side — both within the £20,000 annual allowance.

Last updated: May 2026 · 2026/27 allowances

Contributions

£
£

Annual: £3,600 (£20,000 ISA cap)

Rates & assumptions

%

Top easy-access cash ISAs are around 4–5% in 2026.

%

Global equity long-run nominal return ~7%; volatile year-to-year.

%

Net equity return after fees: 6.50%

%

After 15 years, Stocks & Shares ISA is ahead by

£17,552

+20.2% vs Cash ISA · assuming 7% gross / 6.50% net equity return

Cash ISA

£86,732

Real value (today's money): £55,670

Stocks & Shares ISA

£104,284

Real value (today's money): £66,936

Year by year

Yr 1
£8,905
£9,044
Yr 2
£12,989
£13,359
Yr 3
£17,261
£17,963
Yr 4
£21,729
£22,875
Yr 5
£26,403
£28,116
Yr 6
£31,291
£33,708
Yr 7
£36,403
£39,675
Yr 8
£41,751
£46,042
Yr 9
£47,344
£52,834
Yr 10
£53,194
£60,082
Yr 11
£59,313
£67,815
Yr 12
£65,713
£76,066
Yr 13
£72,407
£84,869
Yr 14
£79,409
£94,262
Yr 15
£86,732
£104,284
Cash ISA
S&S ISA
April 2027 alert: The cash ISA portion of the £20,000 annual allowance falls to £12,000 for under-65s from 6 April 2027 (Autumn Budget 2025). The total £20,000 allowance is unchanged — the difference must go into Stocks & Shares, Innovative Finance, or a Lifetime ISA. Savers 65+ keep the full £20,000 cash limit.

Cash ISA vs Stocks & Shares ISA

A Cash ISA is a savings account with the interest sheltered from tax. The £85,000 FSCS deposit protection applies per banking licence, so your capital is guaranteed up to that limit. Right for:

  • Emergency fund (3–6 months of expenses) — short notice, no capital risk.
  • Money you'll need within 5 years — house deposit, wedding, near-term purchase.
  • Higher-rate taxpayers who'd otherwise pay tax on savings interest above the £500 Personal Savings Allowance.
  • Anyone who simply prefers certainty over potential upside.

A Stocks & Shares ISA holds investments — shares, funds, ETFs — with growth and dividends sheltered from tax. Value can fall as well as rise. Right for:

  • Long horizons (5+ years, ideally 10+) so short-term volatility has time to smooth out.
  • Retirement-style saving where the goal is real growth above inflation, not capital preservation.
  • Anyone using the ISA wrapper to shelter dividends and capital gains they'd otherwise have to track on Self-Assessment.

Over the past 50 years, a globally diversified equity portfolio has delivered around 5–7% real return (after inflation). Cash has generally lost ground in real terms over the same horizon.

Related calculators

Other free UK tools that follow on from this calculation.

ISA Calculator

Tax-free growth on Cash and Stocks & Shares ISAs within the £20,000 annual allowance.

Lifetime ISA Calculator

Project savings with the 25% government bonus for a first home or retirement.

Future Value Calculator

Project how a lump sum or regular contributions grow over time with compound interest.

Inflation Calculator

Adjust values for UK CPI inflation to see the real purchasing power of money.