VAT for Small Business / Lesson 1 of 8
When you must register
You crossed the threshold in March. You had 30 days to notice. Did you?
The short answer
- ✓ The backward test uses any rolling 12 months, not your accounting year
- ✓ The forward test applies if the next 30 days alone will exceed the threshold
- ✓ Zero-rated sales count towards the threshold even though no VAT is charged
- ✓ Register late and you owe the VAT you never charged, out of your own margin
Two separate tests
Registration becomes compulsory if either test is met. Most people know about the first and are caught by the second.
| Test | What it looks at |
|---|---|
| Backward look | Your taxable turnover over any rolling 12 months |
| Forward look | Whether you expect to exceed the threshold in the next 30 days alone |
The rolling 12 months is not your accounting year
This is the single biggest misunderstanding in VAT. The backward test looks at any consecutive 12 months, checked at the end of every month. It has nothing to do with your financial year or the tax year.
Checked at the end of every month:
Feb to Jan under fine
Mar to Feb under fine
Apr to Mar OVER you must register
You have 30 days from the end of that month to notify,
and registration takes effect from the first day of the
month after that. Your accounting year is irrelevant.The forward look is faster and harsher
If at any point you expect your taxable turnover to exceed the threshold in the next 30 days by itself, you must register immediately, and registration takes effect from the date you formed that expectation, not 30 days later.
One large contract can trigger this on the day it is signed, with no rolling history involved at all.
What counts as taxable turnover
Everything you sell that is not exempt, including zero-rated sales. Zero-rated is not the same as exempt: zero-rated sales do count towards the threshold even though no VAT is charged on them.
The bit HMRC does not spell out
Late registration does not just mean a penalty. You are liable for the VAT from the date you should have registered, on sales where you did not charge any. Going back to customers months later asking for an extra 20% is commercially impossible with consumers, so in practice that VAT comes out of your own margin.
A business trading near the threshold should check the rolling figure at the end of every month. It takes two minutes and it is the difference between planning for registration and absorbing a fifth of several months' revenue.
Common mistakes
- Checking against the accounting year. It is any rolling 12 months.
- Forgetting the forward look. One contract can trigger it instantly.
- Excluding zero-rated sales. They count towards the threshold.
- Assuming late registration just means a fine. The unbilled VAT is the real cost.
Try it on your own numbers
This is the same calculator as the full tool page, using 2026/27 rates.
Amount
VAT is calculated instantly as you type. Standard and reduced rates come from current UK VAT settings.
Quick amounts
at VAT
- Net (excluding VAT)
- VAT ()
- Gross (including VAT)
VAT makes up of the gross price. Divide gross by to get the net figure.
Estimate only. Check current VAT rules at gov.uk for your goods or services.
What this means for you
Do this next, in order
Estimates only - not financial or tax advice. Confirm figures on GOV.UK or with an adviser.
Enter your sales and purchases for a VAT period to estimate what you owe HMRC (or reclaim). Enter figures excluding VAT.
VAT on sales (output VAT):
VAT on purchases (input VAT):
- Output VAT (charged on sales)
- Input VAT (reclaimed on purchases)
- −
Standard accounting. Uses the selected VAT rate (). The Flat Rate Scheme below can give a different figure.
On the Flat Rate Scheme you pay a fixed percentage of your VAT-inclusive (gross) turnover and generally cannot reclaim input VAT. Enter your trade's flat rate percentage to compare.
Find your sector's rate on gov.uk (e.g. 12% for many trades; 16.5% limited-cost).
Standard scheme
Output VAT − input VAT
Flat Rate Scheme
% of gross sales
Flat Rate Scheme could save you this period. Standard scheme is cheaper by this period.
Comparison only - eligibility, the limited-cost trader rules and reclaiming VAT on capital assets over £2,000 can change the outcome.
Net vs VAT across amounts
How the net amount and gross (VAT-inclusive) price grow at VAT.
Compare saved scenarios
| Scenario | Net | VAT | Gross | |
|---|---|---|---|---|
Key takeaways
- ✓ The backward test uses any rolling 12 months, not your accounting year
- ✓ The forward test applies if the next 30 days alone will exceed the threshold
- ✓ Zero-rated sales count towards the threshold even though no VAT is charged
- ✓ Register late and you owe the VAT you never charged, out of your own margin
Check you have got it
3 quick questions. No score is kept, and you can change your mind.
1. The backward registration test looks at which period?
2. You sign one contract that alone will exceed the threshold in the next 30 days. What must you do?
3. What is the real cost of registering late?
Sources
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