IR35 Inside vs Outside Decision Kit
The Excel workbook that answers the two questions every UK contractor asks at renewal: Am I really outside IR35? and What's the £-difference to my take-home if the client says inside? Built for the 2024/25 tax year. Complements our free IR35 calculator.
Secure checkout via Gumroad. Instant download after payment. 7-day refund.
Who this is for
You're a UK limited-company contractor or considering going contracting, and you've got an engagement where IR35 status is ambiguous — the client hasn't given a Status Determination Statement yet, or they have and you disagree, or you're weighing an Outside offer against an Inside/umbrella one.
The kit does two things: (1) walks you through a 20-question CEST-style scorecard weighted by the factors HMRC and tribunals actually care about, and (2) shows you side-by-side net take-home across all three routes (Outside/Ltd, Inside/deemed, Umbrella) at your assignment rate.
What's inside — see every sheet
Six connected worksheets. Every number is a live formula pulling from the 2024/25 tax-rate sheet — change your assignment rate once and the entire workbook updates. Screenshots below are actual sheets from the workbook.
1. Start Here
Colour-code legend (blue = your input, black = formula, green = cross-sheet, yellow-highlighted cells are where you type). Recommended reading order. Support & free updates policy. Disclaimer.
2. Decision Scorecard
10 questions weighted by IR35 importance: substitution (up to 3 pts), mutuality of obligation and financial risk (up to 2 pts), control & integration (up to 1 pt). Verdict lands in one of three bands — Inside, Borderline, or Outside — with the specific weak factors flagged so you know what to renegotiate in the contract.
3. Net Take-Home Compare
Three columns, one row per line item: Ltd (Outside) vs Umbrella (Inside). Shows gross assignment income, employer costs (NI + levy + umbrella margin), employee tax + NI, dividend tax where relevant, and net-in-pocket. Verdict names the £ gap between routes.
4. Ltd (Outside) Detail
The optimiser most contractors never build for themselves: director salary + dividend + optional pension contribution, with Corporation Tax marginal relief (19% up to £50k, 26.5% marginal band, 25% above £250k) and proper dividend-tax band-walk. See the exact £ improvement from sacrificing another £5k into pension vs taking it as dividends.
5. Umbrella Detail
The waterfall that umbrellas never show you cleanly: assignment rate → margin → employer NI + apprenticeship levy → gross salary → PAYE income tax + employee NI → net. Change the margin, change the working weeks, watch the net update. The bit most calculators get wrong: your assignment rate is not your gross salary — this sheet solves for the true gross iteratively.
6. Tax Rates 2024/25
All bands, thresholds, NI rates, employer NI, apprenticeship levy, dividend rates, corp tax, dividend allowance — in one reference sheet with named ranges. When HMRC changes rates, you (or we, in the free update) edit one cell and the whole workbook recalculates.
Who this is not for
- You're a PAYE employee thinking about going contracting — this workbook assumes you already understand the Ltd/umbrella structures. Start with our Umbrella vs Ltd inside IR35 explainer first.
- You want a legal opinion on your specific engagement — this is not tax advice. The scorecard is a decision aid; a formal status determination needs a qualified adviser (Qdos, IPSE+, Bauer & Cottrell).
- You're a Scottish taxpayer and want the Income Tax portion to match Scottish bands — the current sheet uses rest-of-UK bands (Scottish variant on the roadmap, free upgrade for buyers).
- You need modelling for Statement of Work vs contract-of-services distinction — that's a legal/contractual question, not a tax-calculation one.
DIY vs Accountant vs This toolkit
| Build it yourself | Contractor accountant | This toolkit | |
|---|---|---|---|
| Cost | Free (your time) | £100 – £150 / month retainer | £19 one-off |
| Time to answer | 4 – 8 hours | 2 – 5 days by email | 2 minutes to plug in numbers |
| Compares all 3 routes at once | Rarely | Not usually — they do your accounts, not your decision | Yes — side-by-side by design |
| Verify the formulas | You wrote them 🤞 | You can't — it's their spreadsheet | Open every formula, edit any input |
| Ongoing (next tax year) | Rebuild from scratch | Still paying the retainer | Free 2025/26 update |
| CEST-style status scorecard | No | Their job is accounts, not status | 20 weighted questions built in |
Why buy it if the free IR35 calculator exists?
The free IR35 calculator answers one question: at this day rate, what's the £-difference between Inside and Outside? It's a great gut-check. The toolkit is what you use when you actually need to make the decision — because it also gives you the status half (the scorecard), the pension optimiser (the Ltd sheet), and the umbrella waterfall line-item you can share with your accountant when you disagree with a client's determination.
Refund policy
7-day, no-questions-asked. Open the workbook, plug in your numbers, and if it doesn't show you at least ten times its price in potential clarity or savings — email [email protected] and we'll refund you.
Disclaimer
This toolkit is for education only. It is not tax advice, legal advice, or a status determination. The scorecard is a decision aid modelled on public HMRC guidance and case law — it does not bind HMRC and it is not a substitute for a formal contract review. Rates and thresholds are for the 2024/25 UK tax year (rest of UK). Always confirm final figures with a qualified accountant or IR35 specialist before acting.
FAQ
Is the scorecard the same as HMRC's CEST tool?
No. CEST is HMRC's own tool and its output is what HMRC will (usually) stand behind. Our scorecard is modelled on the same factors (personal service, mutuality of obligation, control, financial risk, integration) but weighted more like case law does — CEST famously under-weights mutuality of obligation. Use both. If they agree, you have strong evidence. If they disagree, that's your cue to get a paid opinion.
Does the compare sheet handle the off-payroll (Chapter 10) rules?
Yes. Since April 2021 for private-sector medium/large clients, the client decides your status and (if Inside) the fee-payer runs deemed PAYE. The Inside column models that — deemed direct employment income across your income tax + employee NI bands. You get your gross day-rate less all statutory deductions.
Can I model a mixed year — half Inside, half Outside?
Not directly in one row, but the workbook makes it easy: run the Compare sheet twice at different weekly assignments and add the two nets. A "mixed year" tab is on the roadmap.
Does it work for Scottish taxpayers?
The Income Tax portion is currently rest-of-UK (basic 20%, higher 40%, additional 45%). Scotland has 6 bands (19/20/21/42/45/48). A Scottish variant is on the roadmap — buy this and you'll get it free when it ships.
Will it get updated for 2025/26?
Yes. When the March 2025 Budget confirms 2025/26 numbers, we'll ship a free update. You'll get the download link at the same email you bought with.
Why £19?
Cheap enough to be an impulse buy at renewal time. Expensive enough that we can afford to keep updating it every tax year without ads.
Can I share it with my accountant?
Yes — for one buyer's engagements, sharing the file with your own accountant to discuss your decision is fine. Reselling or distributing beyond that isn't. For a firm licence (multiple client scenarios), email [email protected].
Ready to run the numbers on your day rate?
Instant download after checkout. 7-day refund if it doesn't show you at least 10× the price in potential savings or clarity.