AES Ltd — Architecture & Engineering Services
Jason James McCaffreyAES Ltd · Engineering + AI Platform
BIM × AIRATE ENGINE · v2.0jjmccaffrey.com ↗
AES Ltd · 2026/27 · England & Northern Ireland

Rate equivalence.Like for like.

A permanent package is more than its salary. This unwinds one into its parts — bonus, pension, medical cover, paid leave — and rebuilds it as the day rate an inside-IR35 contract would need to match it.

Value received · not value advertised
Permanent package scale — drag to resize £115,800
£40k£220k£395k £575k£750k
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Permanent package

I · Employed
£
%
£
%
%
£
£
days
days
days
Leave and public holidays exceed the working year.

Contract offer

II · Inside IR35
£
hrs
days
£
£
Capped at the £60,000 annual allowance.
Day rate required to match
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Shortfall on offer
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Build-up

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Item Basis Amount

Tax assumptions. England and Northern Ireland, 2026/27. Personal allowance £12,570, withdrawn by £1 for every £2 of adjusted net income above £100,000. Income tax 20% on the first £37,700 of taxable income, 40% to £125,140, then 45%. Employee National Insurance 8% between £12,570 and £50,270, then 2%. Employer National Insurance 15% above £5,000, plus Apprenticeship Levy at 0.5%. Pension contributions are treated as salary sacrifice, so they reduce pay before both tax and National Insurance. Private medical cover is treated as a taxable benefit in kind: the cover is valued in full but income tax is charged on it. No other income, no student loan, no Scottish rates.

What equivalence means here. Total annual value is net cash plus everything reaching you in another form — pension from both sides, and the value of medical and life cover. The required day rate is the figure delivering the same total value across the billable days entered. Because a contractor is not paid for leave, fewer billable days raise the required rate. Employment security, notice periods and sick pay carry real value and are not priced here.

Licence

This calculator is not a public domain program. It is copyrighted by the Author.* This software is protected by United Kingdom copyright law and also by international treaty provisions. The Author grants you a licence to use this software for evaluation and training purposes for an indefinite period. You may not use, copy, rent, lease, sell, modify, decompile, unprotect, disassemble, otherwise reverse engineer, or transfer this software except as provided in this agreement. Any such unauthorised use shall result in immediate and automatic termination of this licence. All rights not expressly granted here are reserved to the Author. You may copy and distribute the unregistered version of this calculator, completely unaltered and with this licence and disclaimer intact, without further permission.

Disclaimer

This software is provided for evaluation and training purposes only, on an "as is" basis. The Author disclaims all warranties relating to this software, whether expressed or implied, including but not limited to any implied warranties of merchantability or fitness for a particular purpose. The Author shall not be liable for any indirect, consequential or incidental damages arising out of the use or inability to use such software, even if the Author has been advised of the possibility of such damages or claims. The person using the software bears all risk as to the quality and performance of the software. Although every effort has been made to ensure the accuracy of this program, users should verify the results for themselves.

Nothing produced by this calculator constitutes tax, financial, employment or legal advice, and it must not be relied upon as such. Tax legislation, rates and thresholds are subject to change, and individual circumstances vary. Users should take advice from a suitably qualified accountant or adviser before acting on any figure shown.

* The Author is Jason James McCaffrey.
Rate Equivalence Calculator, version 3.0 (Swiss Ledger), 2026. © Jason James McCaffrey. All rights reserved.

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