The HMRC Tax Trap: Why You Need a "Tax Stash" (And How Much to Put In It)
It happens to almost every new sole trader. You have a fantastic first year in business. Invoices are getting paid, you’ve upgraded your equipment, maybe you even treated yourself to a well-deserved holiday.
Then January rolls around. Your accountant calculates your Self Assessment, and suddenly you are staring at a massive tax bill that you simply don’t have the cash to pay.
Welcome to the HMRC Tax Trap.
Unlike being an employee where tax is deducted automatically (PAYE), when you run your own business, you receive your income gross. It feels like it’s all yours—but it isn't. A significant chunk of that money belongs to the taxman, and they will come collecting.
Here at Zippy Invoices, we want to help you avoid the dreaded January panic. The solution is simple: The Tax Stash.
What is a Tax Stash?
A tax stash is a separate bank account specifically for your tax liabilities. The golden rule of being self-employed is this: Every time an invoice gets paid, a percentage of that money must immediately move into your tax stash.
Do not leave it in your main current account. Do not use it for "cash flow." If it's out of sight, it’s out of mind, and you won't accidentally spend HMRC's money.
How Much Should I Stash?
As a UK sole trader in the 2026/27 tax year, you are liable for two main things on your profits:
Income Tax (20% basic rate, jumping to 40% if your profits exceed £50,270).
Class 4 National Insurance (6% on profits between £12,570 and £50,270, then 2% above that).
(Note: Class 2 NI is now treated as paid automatically if your profits exceed £7,105, so there's no separate weekly charge to worry about).
Because tax is calculated on your profit (sales minus expenses), not your total sales, the exact percentage you need to save varies depending on your profit margins.
However, a very safe rule of thumb for most new sole traders is to stash 25% to 30% of every invoice.
If your expenses are very low (like a freelance copywriter), aim for 30%. If your expenses are higher (like a tradesperson buying materials), 20-25% might be sufficient.
The Tax Stash Calculator
Want to see what this looks like in practice? Use our calculator below. Enter the amount of an invoice you’ve just been paid, and we’ll show you roughly how much you should immediately transfer to your tax stash to stay safe.
Preparing for MTD (Making Tax Digital)
Building your tax stash is just step one. The next major hurdle for self-employed individuals is Making Tax Digital for Income Tax (MTD ITSA).
Starting in April 2026, if your gross income (your total sales before expenses) is over £50,000, you will no longer do one big annual tax return. Instead, you will need to submit quarterly digital updates to HMRC. (This rolls out to those earning over £30,000 in April 2027).
This means the days of handing your accountant a shoebox full of receipts in December are over. You need digital records, and you need them organised in real-time.
This is where Zippy Invoices shines. By generating and tracking your invoices digitally from day one, you are automatically building the digital trail that HMRC will soon require.
Send the invoice. Get paid. Stash the tax. Sleep easy.