SIPP vs ISA for early retirement in the UK: where should your next pound go?

Why SIPP or ISA is really a question about timing

An early retirement is three different stretches of time, and the two wrappers behave differently in each. Before 57 only an ISA can pay for anything. Between 57 and your State Pension a pension is at its most tax-efficient. After that, the State Pension takes the tax-free allowance and every pension pound is taxed on the way out.

That is why the answer is not one wrapper or the other. A SIPP is a better deal per pound, but a pound you cannot reach on the day you stop work is worth nothing on that day. An ISA can be spent at any age, but every pound in it has already been taxed once. The plan that works uses the ISA for the stretch only it can cover and the pension for everything else.

The date that makes this urgent is 6 April 2028, when the normal minimum pension age rises from 55 to 57 with no phasing. Anyone born after 5 April 1973 will not be able to touch a private pension before 57, which means retiring at 55 now requires two years funded from outside a pension - and retiring at 50 requires seven.

What £100 in a SIPP costs and returns, compared with an ISA

Put £100 into an ISA and it costs you £100 of take-home pay. Put £100 into a pension and it costs a basic-rate taxpayer £80 and a higher-rate taxpayer £60, because the tax you paid on that income is handed back. The catch is on the way out, where three-quarters of a pension withdrawal is taxed as income.

Salary sacrifice widens every one of those gaps because it saves National Insurance as well as income tax, and some employers pass on part of their own NI saving too. It only works through a workplace scheme, not a SIPP you pay into directly, but you can usually transfer from one to the other later. Relief on a SIPP is claimed at source at 20%; a higher-rate taxpayer has to claim the other 20% through Self Assessment, and a surprising number never do.

Notice what the table does not contain: any figure for investment growth. That is deliberate, and it is the next section.

Investment growth does not change the answer

Both wrappers grow free of tax on dividends, interest and capital gains, so the same fund in a SIPP and an ISA grows at exactly the same rate. Growth multiplies both pots equally, which means it cannot move the ratio between them - only tax in, tax out and access can.

Take £300 a month of take-home pay for 20 years on our Balanced assumptions. In an ISA it becomes £88,629 in today's money. The same £300 funds £375 a month in a pension for a basic-rate taxpayer, which becomes £110,786 - and £94,168 once three-quarters of it has been taxed at 20%. Run the same sums at 3% or 7% growth and every figure moves, but the pension still ends 6% ahead.

Nobody has ever beaten an ISA by picking better funds inside a pension. The wrappers are decided by tax and access; the funds are a separate decision, and you can hold the same ones in both.

The practical consequence is that you do not need a growth forecast to make this choice, which is a relief, because growth is the assumption that moves every other retirement number the most. The one place growth does matter is the size of the pot you need in total - and that is the same whichever wrapper it sits in.

The bridge years: where a SIPP is at its most tax-efficient

Between 57 and your State Pension age you have no other income, so your personal allowance of £12,570 is sitting unused. Draw from a pension as lump sums that are 25% tax free and 75% taxable, and £16,760 a year comes out with no tax at all - because three-quarters of it is exactly £12,570.

Once the State Pension starts that allowance is gone. The full new State Pension is £12,548 a year in 2026/27, which leaves just £22 of the personal allowance for anything else. From that point every pension withdrawal loses 15% on the way out. The same pound of pension is worth £1.00 drawn before your State Pension and £0.85 drawn after it.

This flips the way most people think about the two wrappers. The ISA is not the retirement money you spend first because it is flexible. It is the money that pays for the years before 57, and then the money that fills the gap above £16,760 a year, and then the money that is still growing tax free at 75 when the pension has been taxed on every pound. How long a given pot lasts under that drawdown is a separate question, and the answer is the same whichever wrapper it sits in.

How much ISA you need if you stop before 57

Every year between the age you stop and 57 has to be paid for entirely from money with no age lock. At £2,200 a month that is £26,400 a year in today's money, and the table shows how it adds up - and how many years of a full £20,000 ISA allowance it takes to build.

The ISA is not extra money on top of the pot you need. It is part of the same total, deliberately held in the wrapper you can reach. Stopping at 55 needs about £513,473 in all on these assumptions, of which £52,800 - 10% - has to be outside a pension. Stopping at 50 pushes the outside-pension share to 31%, which is why very early retirements are built mostly in ISAs and taxable accounts, whatever the tax relief says.

Two things soften the table. Some of the money can sit in ordinary savings or a general investment account rather than an ISA - it is the age lock that matters, not the wrapper - though outside an ISA you start paying tax on interest, dividends and gains. And a plan that involves any earnings before 57, even a day or two a week, shrinks the bridge fund faster than anything else on this page.

Where the next pound goes, in order

Put the two wrappers together with the tax facts above and a clear order falls out. Work down the list until you run out of pounds.

1. 1Every pound your employer will matchA matched contribution is a guaranteed instant return of 100% before any tax relief, and no ISA can compete with it. If your scheme matches up to a percentage of salary, contribute at least that much, and do it before anything below.
2. 2The ISA bridge, if you plan to stop before 57Work out how many years fall before 57, multiply by a year of spending, and fund that in an ISA first - £52,800 for a stop at 55 on £2,200 a month. The tax relief you give up is the price of being able to stop on the day you choose. If the bridge is bigger than £20,000 a year can build in the time you have, the answer is a later stop date, not a smaller bridge.
3. 3The pension, for every pound of income taxed at 40%A higher-rate taxpayer gets 42% more per pound from a pension than from an ISA if they pay basic rate in retirement, and 47% more through salary sacrifice. That beats almost any other use of the money. Keep going until your contributions have used up the slice of income above the higher-rate threshold - relief above 20% only applies to income that was taxed above 20%.
4. 4A Lifetime ISA, if you are under 40 and the money is for after 60The government adds 25% to up to £4,000 a year, so £4,000 becomes £5,000 - the same uplift as basic-rate pension relief - and it comes out tax free from 60. The same £4,000 in a pension becomes £4,250 after tax at basic rate, or £5,667 with higher-rate relief. So it beats a basic-rate pension, loses to a higher-rate one, and is useless for the bridge: withdrawing before 60 for anything but a first home costs 25%. It counts towards your £20,000 ISA allowance.
5. 5The pension for basic-rate taxpayers too, once the bridge is fundedThe edge is smaller - 6% with relief at source, 18% through salary sacrifice, and 25% on anything you can draw inside the personal allowance before your State Pension - but it is still an edge, and it compounds for decades. The honest counterweight is flexibility: a pension pound is locked until 57, and life between now and then is uncertain. A workable rule is pension for money you are certain is for retirement, ISA for money you might need first.
6. 6Whatever is left goes wherever there is still roomThe pension annual allowance is £60,000 a year including employer contributions and tax relief, and the ISA allowance is £20,000. Few people fill both, but anyone who does has run out of tax shelter and is into general investment accounts - where the order of the three stretches above still applies.

Work out how quickly your ISA bridge builds

The bridge is the one figure in this article that has to be right on a specific date, so it is worth seeing how fast a monthly amount gets there. The calculator below is prefilled with the first worked example: £296 a month for 13 years, shown in today's money.

Three savers, three splits

The order above produces very different splits depending on the stop date and the tax band. All three are aiming at £2,200 a month, already take their full employer match, and are deciding where the next pound of their own money goes.

The rules that can tip the balance

The per-pound maths is the same for everyone. These are the ceilings and exceptions that change it for some people, and most of them bite early retirees harder than anyone else.

• The annual allowance is £60,000. That is the most that can go into pensions in a tax year with tax relief, counting your contributions, your employer's and the relief itself. It tapers for very high earners, and unused allowance from the previous three years can usually be carried forward. Relief is also capped at your earnings for the year.
• Flexibly accessing a pension cuts the allowance to £10,000. Take taxable income from a defined contribution pension and the money purchase annual allowance applies for good. This is the trap for early retirees who go back to work: drawing at 57 and then earning again at 60 leaves you with a fraction of the room to rebuild. The 25% tax-free lump sum on its own does not trigger it.
• Tax-free cash is capped at £268,275. The lump sum allowance limits the total tax-free cash across all your pensions, which is 25% of £1,073,100. Above that pot size the pension's 6% basic-rate edge disappears entirely, and an ISA becomes the better home for basic-rate money.
• Pensions are due to join your estate for inheritance tax. From April 2027 unused pension pots are due to count towards inheritance tax, removing the advantage pensions had over ISAs for money you never expected to spend. For the money you will spend, nothing changes.
• Salary sacrifice has a cap coming. The government has announced that from April 2029 salary-sacrificed pension contributions above £2,000 a year will attract National Insurance. The income tax relief is unaffected, so the salary-sacrifice rows in the table above shrink towards the ordinary pension rows for larger contributions.
• Scotland taxes income differently. Scottish rates and bands differ, with more bands and higher rates above £12,570, so the relief on the way in and the tax on the way out both move. The order of the steps stays the same; the size of the pension's edge changes.

What this comparison deliberately leaves out

Tax rules are the one part of a forty-year plan that is guaranteed to change. Hold the edge figures loosely because of these.

• Future tax rates. Every figure assumes 2026/27 rates on the way out as well as in. The 25% tax-free lump sum, the personal allowance and the basic rate have all been the subject of Budget speculation, and any of them moving changes the pension's edge - though not the access rules that decide the bridge.
• Frozen allowances. The personal allowance has been frozen for years and the State Pension is rising to meet it, which is why the tax-free bridge withdrawal is £16,760 today and could be smaller in real terms by the time you use it.
• Defined benefit pensions. A final salary or career average scheme is a different beast: its value is the income it promises, taking it early means a permanent reduction, and it usually beats both wrappers here. Treat it as income in the bridge and after, and run the maths on what is left.
• Fees. Both figures assume the same charges. A workplace scheme with a negotiated low fee, or a SIPP paying 1% a year, can be worth more than the 6% basic-rate edge over a long enough horizon.
• Means-tested benefits and student loans. Pension contributions reduce the income those are assessed on; ISA contributions do not. For some people at some points that outweighs everything else on this page.

None of that changes the shape of the answer. The bridge has to exist and can only be built in something without an age lock; everything after it is a tax question, and pensions win tax questions. What the total pot has to be is the bigger number, and the split is how you make sure you can spend it.

How to decide for yourself

Frequently asked questions