Spreadsheets have worked for decades. The rules changed in April 2026.
Spreadsheets are the default record-keeping tool for a large proportion of self-employed construction workers. They are familiar, flexible, free and entirely legal for recording CIS income and expenses. For subcontractors with modest turnover, a well-kept spreadsheet has always been a reasonable alternative to dedicated accounting software.
Two things changed in April 2026. First, Making Tax Digital for Income Tax came into force for sole traders and partnerships with gross income over £50,000, requiring digital record-keeping and quarterly updates through MTD-compatible software. A spreadsheet alone does not satisfy those requirements. Second, the nil-return obligation for CIS contractors was reinstated: contractors must now file a CIS300 return every month, including months with no payments, using HMRC's service or recognised software. A spreadsheet cannot do either of those things.
This guide sets out what spreadsheets can still do, where they break, the bridging-software option for MTD compliance, and what the migration to accounting software actually involves.
What you can still do with a spreadsheet in 2026/27
If you are a sole-trader CIS subcontractor with gross income under £50,000, a spreadsheet remains a legal and practical record-keeping method in 2026/27. You are not required to use accounting software. Your obligations are to keep accurate records and file a Self Assessment return by 31 January each year. A well-organised spreadsheet that records your income, expenses and CIS deductions satisfies those obligations.
The following tasks are legitimate uses of a spreadsheet for a CIS worker below the MTD threshold:
- Tracking gross income, the materials element and CIS deducted for each payment received.
- Recording business expenses: van costs, tools, insurance, mileage (at 55p per mile for the first 10,000 business miles from 6 April 2026), protective clothing, phone use and use of home.
- Calculating taxable profit at the end of the year for the Self Assessment return.
- Keeping a log of CIS payment and deduction statements received from contractors.
- Estimating the expected Self Assessment bill or refund during the year.
None of this requires software. The test is whether your records are accurate and retrievable if HMRC asks to see them, not whether they are stored in a particular format. HMRC expects business records to be retained for five years after the relevant 31 January filing deadline.
Where spreadsheets break: four hard limits
There are four things a spreadsheet cannot do for a CIS worker, regardless of how well it is maintained.
1. File the CIS300 monthly return (contractor obligation). If you are a CIS contractor who pays subcontractors, you must file a CIS300 monthly return with HMRC by the 19th of every month following the tax month. A spreadsheet cannot file this. The filing must go through HMRC's CIS online service or HMRC-recognised software. From April 2026 nil returns carry the same obligation and the same penalty ladder (£100 for one day late, rising to £300 or 5% of the CIS liability at six months). A spreadsheet can help you prepare the figures, but the filing step requires something else.
2. Verify subcontractor status (contractor obligation). Before paying a subcontractor for the first time, a contractor must verify their CIS status with HMRC to find out whether to deduct at 0% (GPS), 20% (registered) or 30% (unregistered). This must be done through HMRC's CIS service or through integrated payroll software. A spreadsheet cannot connect to HMRC's verification system.
3. Send quarterly MTD updates (sole traders and partnerships over £50,000 gross). From April 2026, any sole trader or partnership with gross income over £50,000 must send quarterly updates to HMRC through MTD-compatible software. The quarterly update deadline is the 7th of the following month: 7 August, 7 November, 7 February and 7 May. A spreadsheet cannot transmit data to HMRC's MTD systems directly. You need either dedicated accounting software or MTD bridging software.
4. Track VAT domestic reverse charge correctly (VAT-registered contractors). The domestic reverse charge (DRC) has applied to construction services since March 2021. On a reverse-charge invoice, the contractor (customer) accounts for the VAT rather than the supplier. Recording this correctly in a spreadsheet is possible, but the VAT return itself needs to report the amounts in the correct return boxes (boxes 1, 4, 6 and 7). Dedicated accounting software handles the VAT return mechanics automatically. A spreadsheet requires manual calculation and entry for each return.
The MTD gross-income trap for CIS subcontractors
The most common misunderstanding about the £50,000 MTD threshold is how it is measured. It is not the amount you bank. It is your gross income before CIS deductions.
Take a registered subcontractor earning £60,000 gross construction income. Their contractor deducts 20% from the labour element across the year, and the subcontractor banks around £48,000 net. That subcontractor might assume their banked receipts of £48,000 keep them under the £50,000 threshold. They are wrong: the threshold is tested on the £60,000 gross figure, not the £48,000 net, so they are in scope for MTD from April 2026.
The same logic applies at the £30,000 threshold that arrives from April 2027. A subcontractor on £36,000 gross who banks £28,800 after 20% CIS looks comfortably under the £30,000 line on their bank statement, but they are £6,000 over it on the gross figure that HMRC tests.
This matters because a subcontractor who does not realise they are in scope for MTD will continue on a spreadsheet, miss the quarterly update deadlines, and face penalty points accumulating silently. HMRC has confirmed it will not charge late-update penalty points in the first year (2026/27), so a subcontractor who catches this late in 2026/27 can get set up without an immediate penalty consequence. The annual return and payment deadlines still apply, so the grace is narrow.
| Gross CIS income | Net banked (20% deduction rate) | In scope from April 2026? | In scope from April 2027? |
|---|---|---|---|
| £45,000 | £36,000 | No | Yes |
| £50,001 | £40,001 | Yes | Yes |
| £60,000 | £48,000 | Yes | Yes |
| £30,001 | £24,001 | No | Yes |
| £25,000 | £20,000 | No | No |
If you are uncertain whether you are in scope, our guide to Making Tax Digital and CIS covers the threshold calculation and the quarterly update obligations in detail.
MTD bridging software: the spreadsheet user's compliance option
If you are above the MTD threshold and want to remain on a spreadsheet rather than switching to dedicated accounting software, bridging software is the middle option. Bridging software sits between your spreadsheet and HMRC's MTD API. You keep your records in the spreadsheet as normal, and the bridging software reads the relevant figures and transmits them as a quarterly MTD update in the format HMRC requires.
Bridging software for MTD for Income Tax is available from multiple providers, typically at low monthly cost. It is not a permanent solution: HMRC's intention is that taxpayers move to integrated digital tools, and the bridging option may become more restricted in future. But as a transitional measure for a subcontractor who needs to comply with MTD from April 2026 without disrupting their existing record-keeping, bridging software buys time.
The limitation of bridging software is that it only solves the quarterly-update problem. It does not help with CIS300 filing if you are a contractor, does not handle VAT reverse charge, and does not integrate your records with payroll. If those additional needs exist, a full switch to accounting software is the cleaner answer.
When to make the switch: a practical guide
Staying on a spreadsheet makes sense while your situation is simple: sole-trader subcontractor, income under the MTD threshold, no employees, no VAT registration, and not paying subcontractors yourself. The moment any of those conditions changes, the case for accounting software strengthens.
The practical trigger points are:
- Gross income approaching £50,000. If you are consistently earning £45,000 to £55,000 gross, you are likely to cross the MTD threshold in the near term. Getting set up on compatible software before you cross is simpler than retrospectively catching up on missed quarterly updates.
- Starting to pay your own subcontractors. Once you become a contractor who makes CIS payments, you need software or HMRC's service for CIS300 filing. The CIS300 obligation exists from the first payment, not after a threshold is crossed.
- VAT registration. VAT adds a filing obligation (quarterly VAT returns) and, if domestic reverse charge applies to your work, requires correct invoice coding. Software that handles VAT and CIS together reduces the risk of VAT return errors.
- Tax enquiry. If HMRC opens an enquiry into your Self Assessment return, clearly organised digital records held in accounting software are easier to produce and audit than multiple versions of a spreadsheet. This is a risk-management reason rather than a legal requirement.
Moving your records: a practical migration guide
Switching from a spreadsheet to accounting software (QuickBooks, Xero, FreeAgent or another platform) does not require you to re-enter years of historical data. The migration covers the current tax year only.
The migration covers the current tax year only. Steps: choose a start date (ideally 6 April); enter opening balances; import bank transactions via CSV export from your bank; record each income payment with the gross amount, materials element and CIS deducted (your deduction statements are the source, never the net banked figure); enter expenses with receipts attached digitally; and leave prior-year records in their original spreadsheet format, because HMRC does not require historical data to be migrated.
Our guide to CIS accounting software covers what each platform does for CIS workers, including the specific CIS features in QuickBooks, Xero, Sage and FreeAgent. For a comparison of dedicated CIS payroll tools, see our CIS payroll software guide. And for what HMRC expects you to retain and for how long, our CIS record-keeping guide covers the full requirements.
The cost comparison: spreadsheet versus software
| Method | Monthly cost | MTD compliant (over £50k) | CIS300 filing | Time per month (estimate) |
|---|---|---|---|---|
| Spreadsheet only | £0 | No | No | 2-4 hours (manual) |
| Spreadsheet + HMRC CIS online service | £0 | No (unless bridging software added) | Yes (manual) | 3-5 hours |
| Spreadsheet + bridging software | Low (varies by provider) | Yes | No (unless HMRC service added) | 2-4 hours |
| FreeAgent (NatWest/RBS customer) | £0 | Yes | Prepare only (file via HMRC service) | 1-2 hours |
| QuickBooks Simple Start | Around £16 (checked June 2026) | Yes | Yes | Under 1 hour |
| Employment Hero free tier | £0 | Via MTD payroll integration | Yes | Under 1 hour |
Time estimates are illustrative. Manual record-keeping on a spreadsheet is not free in practice: it costs time, and that cost grows as income grows. For a subcontractor earning £55,000 gross, FreeAgent (free for NatWest and RBS customers, £19 per month otherwise) is offset within a few hours of saved administration each month.
The CIS deduction calculator and refund estimator
Whether you use a spreadsheet or accounting software, the two calculations that matter most are how much CIS is being deducted each month and whether you are likely to get a refund at the end of the year. Our CIS deduction calculator shows the deduction on any payment split between labour and materials. Our CIS refund estimator gives you a full-year figure based on gross income, expenses and the deduction rate you are on.
For subcontractors who use spreadsheets, these tools can sit alongside the spreadsheet without requiring a switch: use the calculators for the arithmetic, use the spreadsheet for the record, and review annually whether the volume of work justifies upgrading. And if you are approaching the £50,000 gross threshold, the time to set up software is before the first quarterly MTD deadline you are required to meet, not after.