· ReadyStack
Worked example
Real numbers from this tool, line by line.
£13,725. That is the annual allowance charge a UK finance director on £245,000 owes for 2026/27 - and neither the payslip nor the pension statement says a word about it.
Here are her figures, the ones anybody in that seat can read off a P60 and a benefits statement:
Taxable income (after sacrifice) £245,000 Own contributions (net, at source) £12,000 -> £15,000 gross Employer contributions £60,000 Salary sacrifice (post-8 July 2015) £10,000 Carry-forward 2023/24 + 24/25 + 25/26 £22,000
Threshold income £245,000 - £15,000 + £10,000 = £240,000 (over £200,000) Adjusted income £245,000 + £60,000 + £10,000 = £315,000 (over £260,000) Annual allowance £60,000 - (£315,000 - £260,000) / 2 = £32,500 Pension input £15,000 + £60,000 + £10,000 = £85,000 Over the allowance after £22,000 of carry-forward is used = £30,500 Charge at 45% = £13,725 Higher-rate relief her provider never added = £3,750
Two things in that block are what everyone gets wrong.
The first is the word AND. The tapered annual allowance only bites when threshold income is over £200,000 and adjusted income is over £260,000. Move the same person to £215,000 of income with a £15,000 employer contribution and threshold income is £210,000 - over the line - but adjusted income is £240,000, under it. The allowance stays at the full £60,000 and there is £42,000 of room. Half the panic about the taper is people who failed one test and assumed that was enough.
The second is the £3,750. A relief-at-source contribution gets 20% added by the provider automatically. The rest - another 20% for a higher-rate taxpayer, another 25% for an additional-rate one - only arrives if you ask for it on a Self Assessment return. Nobody sends it to you. On a £15,000 gross contribution at 45% that is £3,750 sitting unclaimed. Between £100,000 and £125,140 it is worse: the contribution also hands back the personal allowance you were losing at £1 for every £2, so £15,000 gross is worth £6,000 of extra relief - a 60% effective rate on that slice.
And there is a clock. Unused allowance carries forward three tax years. The 2023/24 amount is used in 2026/27 or it is gone after 5 April 2027. In the second example above that is £9,000 that quietly expires.
HMRC's own calculator answers the allowance question. It does not tell you the relief you never claimed, and it does not show the personal allowance you get back. A chatbot will happily apply one income test instead of two. So the extension does both, on the 2026/27 figures - £60,000 allowance, £200,000 and £260,000 thresholds, £10,000 floor, £10,000 money purchase annual allowance - and it does the arithmetic inside your own browser, because the input is your salary and it has no business leaving the machine.
Free version: the whole calculation, unlimited, no key, nothing held back. If you want the working as a .csv to hand your accountant or file with your records, that is the $60 version. An accountant charges £150-400 plus VAT to prepare the return this all feeds into.
15 seconds — what it actually does
Questions people ask
What does this extension actually work out?
It takes your 2026/27 income and pension contributions and returns four numbers: your annual allowance after the taper, how much carry-forward from the last three years you have left, any excess and the charge it triggers, and the higher-rate or additional-rate relief you can still claim on your Self Assessment return.
Who is this for?
UK employees, directors and partners paying 40% or 45% tax, particularly anyone whose bonus pushes adjusted income over £260,000, anyone paying into a SIPP from taxed income, and anyone who has flexibly accessed a pot and is now inside the £10,000 money purchase annual allowance.
HMRC has a calculator. Why do I need this?
HMRC's calculator answers the allowance question only. It does not tell you the higher-rate relief your provider never added, and it does not show the personal allowance you recover between £100,000 and £125,140 - the 60% band where a contribution is worth most. This does both in one screen.
What is free and what costs money?
Every calculation is free, unlimited, with no key and no watermark. The paid version ($60 once) adds one thing: exporting your inputs and results as a .csv so you can hand the working to an accountant or keep it with your tax records. The answer itself is never withheld.
What would this cost me otherwise?
An accountant charges roughly £150-400 plus VAT to prepare a Self Assessment return in 2026, and a dedicated annual allowance review costs more. A single missed higher-rate claim on a £15,000 contribution is worth £3,750 to an additional-rate taxpayer.
Ask about this tool
One question, answered by the person who built it. Your email only if you want the answer sent.