ISA vs Pension for Additional Rate Taxpayers in 2026/27: Where Should the Next £1,000 Go?

Why This Calculation Is Different at the Top

For a basic rate taxpayer, the ISA-vs-pension decision often comes down mainly to access flexibility, since the tax relief gap (20% pension relief vs ISA's no relief but tax-free growth) is relatively modest. For an additional rate taxpayer, the numbers are bigger in every direction — the pension relief is worth more, but so are the risks of falling foul of the annual allowance taper or the Lump Sum Allowance.

The Pension Relief Advantage at 45%

This means an additional rate taxpayer effectively gets £1,000 in their pension for a net outlay of £550 — a relief rate no ISA can match, since ISAs offer no contribution relief at all. The trade-off is access: pension money is locked until at least age 55 (rising to 57 from April 2028), and withdrawals beyond the 25% tax-free lump sum (up to the Lump Sum Allowance of £268,275) are taxed as income at your marginal rate in retirement.

The Annual Allowance Taper: Check This First

Before assuming you can fully use pension relief, check whether the tapered annual allowance affects you:

Many additional rate taxpayers (income above £125,140 but below £260,000) are entirely unaffected by the taper and can use the full £60,000 annual allowance. It's specifically higher earners — particularly those with employer contributions, bonuses, and benefits pushing "adjusted income" (which includes employer pension contributions, unlike "threshold income") above £260,000 — who need to check this carefully, since exceeding the tapered allowance triggers an Annual Allowance Charge, effectively clawing back the tax relief.

The 60% Trap: £100,000–£125,140

This band deserves special attention because it produces the highest effective marginal rate in the UK tax system for many earners:

A pension contribution that brings adjusted net income back below £100,000 can restore some or all of the personal allowance — meaning the effective relief on contributions within this specific band can exceed even the 45% additional rate relief available above £125,140. Anyone with income in the £100,000–£125,140 range should prioritise pension contributions specifically to escape this band before considering contributions purely for standard 45% relief above it.

When an ISA Makes More Sense

Despite the strong pension relief case, ISAs remain valuable for additional rate taxpayers in specific situations:

• Money you might need before pension access age — an ISA offers full access at any time, tax-free, with no penalty
• Once annual allowance headroom is used or tapered close to the £10,000 minimum — further pension contributions become less attractive relative to the ISA allowance (£20,000/year in 2026/27)
• As a hedge against future pension tax rule changes — pension tax treatment has changed materially in recent years (Lifetime Allowance abolition, inheritance tax on pensions from 2027); an ISA's tax-free treatment is comparatively stable and simple
• Once you're near or above the Lump Sum Allowance (£268,275) — very large pension pots start to reduce the proportional value of further contributions, since more of any future lump sum withdrawal may fall outside the tax-free portion

A Practical Default for Most High Earners

For most additional rate taxpayers with contribution headroom in both:

1. Prioritise pension contributions enough to escape the £100,000–£125,140 personal allowance taper band, if your income falls there.
2. Use further pension contributions up to your available annual allowance (checking the taper if adjusted income exceeds £260,000), particularly via salary sacrifice where available, which also saves National Insurance.
3. Fill the ISA allowance (£20,000/year) for money you may want access to before pension age, or simply to diversify the tax treatment of your long-term savings.
4. Reassess annually — income, bonus timing, and pension pot size relative to the Lump Sum Allowance can all shift the optimal split from one tax year to the next.