The smallest pension contribution that brings adjusted net income back under it, and what that costs.
Two lines in the UK tax system cost more to cross than the pound that crosses them. At £100,000 of adjusted net income the Personal Allowance starts to go, which makes the next £25,140 some of the most expensive income in the system (an effective 60% before National Insurance), and the free childcare hours and Tax-Free Childcare are lost at the same point. At £60,000 the High Income Child Benefit Charge starts, and claws the benefit back by £80,000. Both are measured on adjusted net income, not salary, and both are tested on one person, never on the household. That is what this page works with: a pension contribution from gross pay lowers the figure the line is measured on, pound for pound in a salary sacrifice or net pay scheme.
What it solves for
The smallest contribution that brings adjusted net income to the line you pick, not a pound more, checked through the engine rather than assumed. Then what that costs in take-home, which is a good deal less than the contribution because the tax and National Insurance that would have been charged on that pay are not charged. Someone on £70,000 with two children who moves £10,000 into a pension by salary sacrifice gives up £5,800 of take-home pay and keeps £1,169 of Child Benefit that the charge was taking, so the year’s cost of clearing the line is £4,631. The result shows all three numbers, and the working under it shows every line of the sum.
What it does not decide
Whether to do it. The contribution is not lost, but it is locked: it goes into a pension, where it is invested and can fall in value, and it cannot normally be touched until the minimum pension age. Whether that trade suits a household turns on things this page cannot see, including whether the employer offers salary sacrifice at all, whether there is room under the pension annual allowance, and whether the pay can be spared now. The result says so in as many words, and then leaves the number with you.
What this is, and what it is not
It is arithmetic about the 2026/27 rules for employment income under PAYE, with every figure it used listed under the result and the date it was last read against its source. It is not advice. Relief-at-source pensions, where the tax relief is added to the pot, are not modelled, because the amount that reduces adjusted net income there is the grossed-up figure and a rough version would be wrong at the line; Gift Aid lowers the figure too and is not modelled either. If the amount involved is large, that is a conversation with a regulated adviser (the FCA Register lists them) or, free, with MoneyHelper. For the childcare side of the £100,000 line in particular, this is the page that finds it; for what a rise is worth once a line sits inside it, value the rise first.
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