Card spending gets tracked almost by accident — it's sitting in a bank app whether you log it or not. Cash doesn't have that safety net. A float in the van, a fiver handed over for two hours of labouring, change from the trade counter — it all gets spent on the job and none of it leaves a paper trail unless you make one.
What "petty cash" actually covers on a tradesman's job
- A working float — cash kept on hand for small, immediate job costs.
- Cash labour — paying someone cash for a few hours' help, which may still fall under CIS depending on the arrangement.
- Parking, tolls and meters — rarely card-only, almost never logged.
- Small trade counter buys — a box of screws, a tube of sealant, paid in coins because it's quicker than tapping a card for £3.40.
- Tips and odd cash-in — cash a client hands over on the day, which still needs recording as income.
None of it is large on its own. Across a job, it's routinely £50–£150 that never makes it into any record at all.
Why a cash tin and a notebook don't survive contact with a real job
The plan always starts well: write it in the notebook as it happens. By week two, the notebook's in the van under a dust sheet, half the entries are guessed from memory, and the float total never matches what's actually in the tin. It's not a discipline problem — it's that paper cash books were never built for someone with muddy hands standing in the rain.
What a petty cash app actually needs to do
- Log cash the same way as receipts — one feed, not two separate systems to reconcile later.
- Tag every cash entry to a job — cash spent on Job A shouldn't blur into Job B's totals.
- Track a running float balance — so you know what's left in the tin without counting it.
- Work without a card or a bank feed — cash has no transaction to import, so it needs manual entry that's actually fast.
- Flag cash paid to labour — for CIS purposes, so it isn't lost among materials spending.
- Export cleanly — an accountant needs to see cash in and cash out just as clearly as card spending.
| Method | What actually happens |
|---|---|
| Cash tin, no log | Float slowly drains with no record of where it went. |
| Paper cash book | Accurate for a week, abandoned once the pages get wet or lost. |
| Spreadsheet | Needs typing up later, so cash entries get forgotten before they're recorded. |
| App with cash entries (like Site Wallet) | Logged in seconds on-site, tagged to the job, rolled into the same total as receipts. |
A worked example
Say you start a job with a £150 float. Through the week: £20 for parking across three site visits, £60 cash to a labourer for a day's help, £15 at the trade counter for fixings, and £8 in odds and ends. Logged against the job as it happens, that's £103 of tracked job cost — and £47 left in the float, matching what's actually in the tin. Without logging it, you'd only know the float's gone, not where.
How Site Wallet handles it
Cash entries sit in the exact same feed as scanned receipts — add an amount, tag the job, done in a few seconds. Every entry rolls into the job's running total alongside card spending and receipts, so the true cost of a job includes cash the moment it's spent, not weeks later from memory. Come tax time, cash and card exports sit side by side, so nothing gets left out of the records HMRC expects you to keep.
FAQ
Do I need a receipt for every small cash purchase?
Where you can get one, keep it — but for genuinely small cash spends without a receipt, a logged entry with the date, amount and what it was for is far better than nothing, and far better than trying to remember it months later.
Does cash paid to a mate for a day's help need to go through CIS?
It depends on the working relationship — genuinely casual, one-off help is treated differently from a sub-contractor arrangement. If in doubt, check with your accountant, but either way the payment itself should be logged against the job.
Is cash a client hands me still taxable income?
Yes — cash income is treated the same as any other income for tax purposes. It should be logged and declared just like a bank transfer or card payment.