Do You Actually Need to Register for VAT?
The short answer is: only if your turnover hits the threshold. As of April 2024, that threshold is £90,000. But here's the thing that catches people out. That figure applies to your total sales in a rolling 12-month period. It doesn't matter if you hit it in January or December. Once you cross it, you have 30 days to tell HMRC.
If you run a double glazing business, you're likely to hit this figure faster than many other trades. A single large commercial contract can push you over. A kitchen extension project with replacement windows for a London terrace house might cost the customer £8,000 to £12,000. Do a handful of those jobs per month, and you're over the limit within weeks.
You can register voluntarily even if you're below the threshold. Some businesses do this to reclaim input VAT on materials and equipment. If you're buying double glazing frames, installation tools, and van insurance, that VAT adds up. Registration might actually put money back in your pocket. The trade-off is more paperwork and quarterly returns to HMRC.
What Happens When You Cross the Line
Let's say your double glazing installation business does £75,000 in the first eight months. Then you land a large contract, worth £18,000. You've now hit £93,000. You must register within 30 days of the end of the month in which you crossed the threshold.
Miss this deadline and HMRC will charge a penalty. It starts at £400 and can climb to £1,000 or more, depending on how late you are. Worse still, you become liable for VAT on sales made before registration. That's money you've already invoiced without collecting VAT. You now owe it out of your own pocket.
Some business owners don't realise this until they're audited months later. By then, a customer who paid £10,000 for windows and fitting becomes a problem. You can't ask them to pay VAT retroactively. You absorb the cost.
The Registration Process, Step by Step
The process is straightforward but requires attention to detail.
- Register online through the HMRC portal. You'll need your National Insurance number, business address, and recent turnover figures.
- Provide details of your business. For a double glazing firm, you'll declare your main activity. HMRC classifies it under building installation and fitting.
- Confirm your intended registration date. This is usually the first day of the month in which you applied or the date you crossed the threshold, whichever is later.
- Receive your VAT registration number. This arrives within a few weeks. You'll need it on all invoices from that date onward.
The entire application takes around 15 minutes online. HMRC usually processes it within two to three weeks. You can register by post if you prefer, but online is faster.
What Changes Once You're Registered
Your invoices must now include your VAT registration number. Every invoice you issue must show VAT as a separate line item. If you're charging £1,200 for a window installation, you'll invoice £1,440 including VAT at 20%. That extra £240 belongs to HMRC, not to you.
You'll file VAT returns every three months. Each return covers a three-month quarter. You declare the VAT you've charged customers and the VAT you've paid on business purchases. The difference is what you owe HMRC or what they owe you.
Here's where many small businesses get caught out. If you've charged £48,000 in sales over three months, you've collected £9,600 in VAT. But if you've spent £18,000 on frames, seals, and fittings, you can claim back £3,600 in input VAT. You owe HMRC £6,000. That's due 30 days after the quarter ends. If you've already spent that money on operating costs, you're short of cash.
This is why cash flow planning matters for newly registered businesses. Some companies set aside VAT as they charge it, treating it as a separate account. Others struggle because they assume all the money they collect is profit.
Record Keeping and Compliance
Once registered, you must keep records for at least six years. These include invoices, receipts, bank statements, and any documents that show business transactions. HMRC can request these on audit.
You don't need specialist software, though most accountants recommend it. Basic spreadsheets work if you're careful, but cloud-based accounting packages are affordable now. Many cost less than £20 per month and handle VAT calculations automatically.
If you're filing late returns or submitting incorrect figures, penalties accumulate. Lateness penalties start at 5% of the VAT you owe. Accuracy penalties apply if figures are wrong. These are serious. Plan your filing calendar and mark quarterly deadline dates in advance.
The Exceptions and Edge Cases
Some supplies are VAT-exempt. If you fit replacement windows for a residential property where the building work is zero-rated, the labour might also be zero-rated in certain circumstances. However, materials you supply are typically standard-rated. The rules are complex and business-specific. Check with your accountant before assuming any supply is exempt.
If you work across the EU, post-Brexit rules apply. You'll need to understand import VAT and Brexit-related compliance. This goes beyond the scope of basic registration, but it's worth knowing that cross-border work brings extra complexity.
Final Thoughts
VAT registration isn't complicated, but it does require systems and discipline. For a double glazing business, it's inevitable if you're successful. Your business is growing, which is good news. The VAT side is just administration. Treat it seriously from day one, get the right accountant, and it becomes routine.
The key mistake is ignoring the threshold. Watch your turnover. When you're within £10,000 of the limit, start preparing. Sort your records, set up your accounting system, and plan for the VAT cash requirement. Do that, and VAT becomes a non-issue.
