ISA vs pension in your 40s: a decision framework for higher earners

I've been sitting with this question for a few months now, partly because I keep getting versions of it from people in their early-to-mid 40s who are finally earning good money and feel vaguely guilty that they haven't "sorted it out" yet. The ISA vs pension debate sounds simple on the surface — tax-free growth now versus tax relief now — but for people earning between £60,000 and £100,000, there are two specific wrinkles that change the calculation dramatically: the personal allowance taper and the high income child benefit charge. I'm going to work through the decision tree here as honestly as I can, including the parts where I think the answer is genuinely "it depends." I'll flag where I'm still working things out, and I'll be specific about numbers because abstract principles aren't actually that useful when you're staring at a payslip wondering what to do next.

the taper: the thing that changes everything between £100k and £125,140 ¶

If your adjusted net income sits between £100,000 and £125,140, your personal allowance is being withdrawn at 50p for every £1 of income over £100,000. The full allowance is £12,570. Once your income hits £125,140, it's gone entirely. What this means in practice is that income in that band is effectively taxed at 60% — you're paying 40% income tax plus losing 20p of allowance worth another 20p of tax. That is an extraordinary marginal rate and most people I speak to don't clock it until I draw it out for them. A pension contribution that brings your adjusted net income from, say, £110,000 back below £100,000 is doing double duty: it's getting 40% relief and it's restoring your personal allowance. The effective relief rate in that scenario is closer to 60%, which makes a pension contribution almost inarguably better than an ISA contribution made from the same pound. The ISA just can't compete with that arithmetic. This isn't a close call.

child benefit and the high income charge: the other taper people forget ¶

The high income child benefit charge (HICBC) kicks in when the higher earner in a household has adjusted net income above £60,000, and it withdraws child benefit at a rate of 1% for every £100 of income above that threshold. By £80,000, 100% of child benefit is clawed back. For a family with three children, child benefit in 2024–25 is roughly £3,094 per year. Losing all of that is equivalent to an extra marginal tax rate of around 15% on that £20,000 band of income — on top of your income tax. Combined with income tax and National Insurance, the effective marginal rate in the £60,000–£80,000 band for someone with children can nudge past 60% when you stack everything up. A pension contribution that pulls adjusted net income below £60,000 stops the charge entirely and restores the full child benefit. This is a concrete, calculable number. I'd encourage anyone in this band with children to sit down and work out exactly how much child benefit they're forgoing, because it often makes the pension case decisive.

so when does the ISA actually win? ¶

I want to be honest here rather than just cheerleading pensions, because there are real situations where the ISA is the better tool. The main one is liquidity. A pension is locked away until at least age 57 (rising from 55 to 57 in 2028). If you're 42 and genuinely uncertain about your career, might want to take a sabbatical, or are building toward early semi-retirement, having money you can actually access in your late 40s or early 50s matters. An ISA lets you do that. The second scenario is if you're already making full use of employer pension contributions and topping up to a point where your total pension pot is approaching the annual allowance ceiling (£60,000 in 2024–25, or your relevant UK earnings if lower). The ISA becomes the natural overflow valve. And if your income is, say, £62,000 and you have no children, the maths are closer — you're getting 40% relief on pension contributions, which is good, but you're not rescuing a taper or child benefit, so the liquidity trade-off becomes more meaningful. I'd still probably lean pension first in that scenario, but I can see the case going the other way for someone with specific near-term plans.

the decision tree: a rough sequence I'd actually use ¶

Start here: are you earning over £100,000? If yes, pension contributions that bring adjusted net income below £100,000 are almost always the priority — the 60% effective relief is hard to argue against. Next question: do you have children and does the HICBC apply? If yes and your income is between £60,000 and £80,000, model the pension contribution that restores your child benefit and treat that as part of the return. Third: have you used your carry forward allowance? You can carry forward unused pension annual allowance from the previous three tax years, which means some people in their 40s can make a very large lump-sum pension contribution in a single year — useful if you've recently had a salary jump. Fourth: what's your liquidity position? If you have less than three to six months of expenses in accessible savings, that has to come first regardless of the ISA-pension debate. Only once those questions are answered does the straight ISA-vs-pension comparison become the main event.

adjusted net income: the number you actually need to know ¶

I find a lot of confusion comes from people not knowing what adjusted net income actually means, so quickly: it's your gross income minus personal pension contributions (the gross amount, not just what you paid net of tax relief). So if you earn £105,000 and make a £6,000 net pension contribution (which becomes £7,500 gross with basic rate relief added), your adjusted net income is £97,500, not £105,000. That matters enormously for both tapers. Employer contributions don't count for this calculation — only personal contributions do. This is why salary sacrifice can be particularly clean: contributions made via salary sacrifice reduce your gross pay before it's reported to HMRC, so the reduction in adjusted net income is immediate and mechanical. If your employer offers salary sacrifice, use it. If they don't, make sure you're claiming the higher rate relief through your self-assessment return.

what I'm still uncertain about ¶

A few things I genuinely haven't fully resolved in my own thinking. First, the future of pension tax relief: there's been persistent speculation for years that higher rate relief could be capped or moved to a flat rate. I don't think you should make decisions based on policy risk alone — the current rules are the current rules — but it's worth noting that the ISA's tax treatment is arguably more politically durable. Second, the pension lifetime allowance was abolished in April 2024, which removed a ceiling that used to make large pension pots complicated. That's broadly good news for higher earners who want to keep contributing, but the rules around death benefits and lump sum allowances are still settling, and I'd encourage anyone with a pot over £500,000 to take specific advice rather than relying on general frameworks like this one. Third, I think the emotional dimension of pensions is underrated — some people genuinely find it easier to save when the money is locked away. That's not irrational, and it's okay to weight it.

a worked example that might be familiar ¶

Say you're 44, earning £95,000, two children receiving child benefit of about £2,212 per year (two children, 2024–25 rates). At £95,000, you're within the HICBC taper — you've lost 35% of your child benefit, roughly £774. You're also within the personal allowance taper: £95,000 is £0 below the £100,000 threshold, so no allowance has been withdrawn yet, but you're close. A pension contribution of £5,000 net (£6,250 gross) reduces adjusted net income to £88,750. That restores some child benefit — the 35,000 climb from £60k to £95k becomes a £28,750 climb, so you claw back around £431 of child benefit annually. The pension contribution also gets 40% tax relief, making the real cost of that £5,000 net contribution around £3,000 out of pocket when you account for both the relief and the child benefit restored. That's a meaningful difference. Run the numbers for your own income and family size — the HMRC tax calculator is genuinely useful for this and I'd suggest using it before making any decisions.

I think the main thing I want to leave you with is that this isn't a question with one right answer, but it's also not as murky as it can seem. The taper zones are mathematically precise, and if you know your adjusted net income, you can work out where you sit and what a pension contribution actually buys you. If you're in the £100k–£125,140 band with children, the pension case is very strong. If you're in the £60k–£80k band with children, it's still strong but the liquidity question matters more. Everywhere else, it's a genuine trade-off worth thinking through slowly. I keep updating my thinking on this as the rules change, so I'll probably revisit this note after the next Budget.