01

The personal savings allowance — who it helps and where it runs out

The personal savings allowance (PSA) was introduced in April 2016 and allows UK taxpayers to earn a defined amount of savings interest tax-free each year. Basic rate taxpayers receive a PSA of £1,000. Higher rate taxpayers receive £500. Additional rate taxpayers (income above £125,140) receive no PSA at all.

The PSA is applied after all other income tax calculations — it is a deduction from savings income, not from total income. It covers interest from bank accounts, building societies, cash ISAs (though ISA interest does not use up the PSA — it is separately exempt), bonds, gilts, peer-to-peer lending and NS&I products.

At the best savings rates available in April 2026, the PSA runs out at the following savings balances: basic rate taxpayer (£1,000 PSA at 4.90% best easy access rate): PSA exhausted at £20,408 of savings. Higher rate taxpayer (£500 PSA at 4.90%): PSA exhausted at £10,204 of savings. Additional rate taxpayer (£0 PSA): every penny of savings interest is taxable from the first pound.

Below these thresholds, a basic rate taxpayer's savings interest is entirely within the PSA — the taxable easy access account at 4.90% and the cash ISA at 4.55% produce the same after-tax return (both zero tax). The taxable account wins on headline rate alone. Above these thresholds, the ISA advantage emerges and grows with the savings balance.

02

The net-of-tax return comparison — the calculation every higher rate taxpayer must run

The comparison between cash ISA and taxable savings must be made on a net-of-tax basis for each taxpayer's marginal rate. The following worked examples demonstrate the correct method.

Higher rate taxpayer, £50,000 savings, April 2026 rates: Option A — Best taxable easy access at 4.90%: gross interest = £2,450. PSA used: £500. Taxable interest: £1,950. Income tax at 40%: £780. Net interest received: £1,670. Net rate: 3.34%. Option B — Best cash ISA at 4.55%: gross and net interest = £2,275. Net rate: 4.55%. Conclusion: the cash ISA generates £605 more per year despite its lower gross rate. The ISA wins by 36% on a net-of-tax basis.

Additional rate taxpayer, £50,000 savings: Option A — Taxable easy access at 4.90%: gross interest = £2,450. Zero PSA. Income tax at 45%: £1,102.50. Net interest: £1,347.50. Net rate: 2.70%. Option B — Cash ISA at 4.55%: net interest = £2,275. Net rate: 4.55%. Conclusion: the cash ISA generates £927.50 more per year — the ISA wins by 69% on a net-of-tax basis.

For higher and additional rate taxpayers, the gross rate advantage required for a taxable account to match a cash ISA is so large that no risk-free savings product achieves it. A higher rate taxpayer needs a taxable account paying 7.58% gross to match a cash ISA at 4.55% net (because 4.55% ÷ 0.60 = 7.58%). This rate does not exist in instant access savings.

03

The ISA allowance — maximisation strategy and the flexible ISA advantage

The annual cash ISA allowance is £20,000 per person — the same as the stocks and shares ISA allowance, and the total ISA allowance covers both combined. A person cannot contribute more than £20,000 across all ISA types in a single tax year. The allowance is use-it-or-lose-it — unused allowance from previous years cannot be carried forward.

For higher rate taxpayers with significant savings, maximising the ISA allowance before 5 April each year is the single most important annual financial action. A higher rate taxpayer who fails to use their £20,000 ISA allowance for five consecutive years loses £100,000 of potential tax-free wrapper capacity — worth approximately £780 per year in saved income tax on the missed deposits at 4.55% cash ISA rate and 40% tax.

Flexible ISAs: several providers (Chip, Plum, Moneybox, Trading 212) offer flexible cash ISAs that allow withdrawal and re-deposit within the same tax year without the re-deposited amount counting as a new subscription. A standard cash ISA does not allow this — once withdrawn, the amount is treated as a new contribution if redeposited. A flexible cash ISA with a £20,000 balance: if £5,000 is withdrawn in July and redeposited in September, the full £20,000 subscription capacity is restored — the withdrawal and redeposit are transparent. This makes flexible ISAs significantly more practical for savers who need occasional access to ISA funds.

ISA transfers: funds accumulated in previous years' cash ISAs can be transferred to a new provider offering a better rate. The transfer preserves the ISA status of the funds — they do not count as a new subscription. ISA transfers must be initiated through the receiving provider, not by withdrawal and redeposit. Current year subscriptions can be transferred in full (the entire current year's contribution must move together) or the transfer can cover only previous years' accumulations.

04

Fixed rate cash ISAs — when locking in makes sense

Fixed rate cash ISAs pay a guaranteed rate for a defined term (typically 1, 2 or 3 years) in exchange for restricted or no access to the funds during the term. As of April 2026, the best fixed rate cash ISA rates are: 1-year: 4.75% (Cynergy Bank, Paragon Bank); 2-year: 4.60% (Shawbrook Bank, Charter Savings); 3-year: 4.45% (Aldermore Bank).

For higher rate taxpayers, the fixed rate cash ISA comparison with taxable fixed bonds is even more decisively in the ISA's favour than the easy access comparison. Best taxable 1-year fixed bond: 4.80% gross. Higher rate taxpayer net rate: (£4,800 - £500 PSA) × 40% = £1,720 tax. Net interest: £3,080. Net rate: 3.08% on £100,000. Best 1-year fixed cash ISA: 4.75% tax-free. Net rate: 4.75%. The ISA generates £1,670 more per year on £100,000 despite only a 0.05% lower gross rate.

The lock-in risk: fixed rate cash ISAs restrict access during the term — typically no withdrawals allowed, or with a penalty of 60 to 180 days of interest. Choose a fixed rate cash ISA only for funds that genuinely will not be needed during the fixed term. Holding some funds in an instant access cash ISA alongside a fixed rate product provides flexibility without sacrificing the fixed rate return on the locked portion.

Rate direction and the fix-now decision: with the Bank of England expected to continue cutting rates through 2026, locking in 4.75% for 12 months now guarantees this return regardless of any cuts. If the Bank cuts by a further 0.50% by October 2026, instant access ISA rates will follow — the 1-year fix captures the current rate premium for the full 12 months.

05

The stocks and shares ISA versus cash ISA decision for long-term savers

For savings with a horizon of five years or more, the stocks and shares ISA investing in global equity index funds significantly outperforms the cash ISA. The long-run real return from global equities of approximately 5 to 7% per year after inflation compares with the cash ISA rate that is likely to fall to 3 to 3.5% by 2027 as the Bank of England continues its rate-cutting cycle.

The cash ISA is the correct choice for: emergency fund overflow above the personal savings allowance threshold; savings earmarked for a specific purpose within five years (property purchase, car, school fees); and savings for investors who cannot tolerate any capital risk in the relevant portion of their wealth.

The stocks and shares ISA is the correct choice for: wealth building over five or more years; pension supplement savings where the pension wrapper is already maximised; and investors who understand and can tolerate equity market volatility in exchange for higher expected long-run returns.

For savers who maximise the cash ISA but have not opened a stocks and shares ISA: the two can coexist within the £20,000 total annual allowance. A contribution of £10,000 to a cash ISA and £10,000 to a stocks and shares ISA uses the full allowance and provides both the capital protection of cash and the growth potential of equities. The optimal split depends on the individual's time horizon, risk tolerance and existing cash reserves.