The monthly sales tax return, in the order we actually do it

Every late filing we have been called in to rescue had the same shape. Nobody misunderstood the law. Somebody could not find three invoices, the bank had not been reconciled since the quarter before, and the person who knew where the purchase records lived had left in March.

So the checklist below is not about tax rules. It is about getting the records into a state where the return takes an afternoon instead of a week. We run it in this order because each step depends on the one above it.

Day 1 — close the sales side

Start with revenue, because it is the number you can least afford to get wrong and the one your customers can contradict.

• Pull every sales invoice for the period, including the ones raised manually.
• Check the numbering runs unbroken. A gap is either a cancelled invoice that was never recorded as cancelled, or an invoice issued outside the system.
• Separate taxable from zero-rated and exempt supplies. Do this now, not at the end — it is the split that drives the whole return.
• List credit notes separately. They reduce output tax, and they are the single most commonly forgotten item.

Where it breaks: invoices raised outside the accounting system. Somebody issues one from a Word template to close a deal on a Friday, and it never reaches the ledger. If your sales team can raise an invoice without the system knowing, that is the first thing to fix, and it is a process fix, not an accounting one.

Day 1 — reconcile the bank before anything else

This is the step people skip, and it is the reason the other steps take so long. An unreconciled bank account means you cannot trust a single figure that follows.

Match every line. Anything unmatched falls into one of four buckets: an invoice you have not raised, a bill you have not recorded, a transfer between your own accounts, or an error. Clear them in that order. Do not leave a suspense account to deal with later. Later is the day before the deadline.

Day 2 — purchases and input tax

Input tax is where most of the money is, and where most of the risk sits.

• Every claim needs a valid tax invoice in your hands. Not a quotation, not a delivery note, not a bank statement line. If the document is missing, the claim waits for the next period.
• Check the supplier's registration number is live. Claiming against a deregistered supplier is an adjustment you will make later under worse conditions.
• Strip out anything not claimable — entertainment, private use, blocked categories.
• Apportion the mixed-use items. Keep the basis of apportionment written down, because you will be asked for it and you will not remember.

Where it breaks: expense claims. Someone pays for something personally, gets reimbursed, and the receipt is a card slip rather than a tax invoice. That is not claimable, and a year of it adds up to a number worth arguing about.

Day 3 — adjustments nobody remembers

These are the items that do not appear in the day-to-day ledger and have to be looked for deliberately:

• Bad debt relief on invoices now old enough to qualify.
• Credit notes issued against a prior period.
• Goods taken for own use or given away.
• Imports, and the tax paid at the border rather than to a supplier.
• Reverse-charge items on services bought from abroad — easy to miss precisely because no supplier invoice carries the tax.

Day 3 — the two checks before you file

Two reconciliations catch almost everything.

Output tax against revenue. Take declared revenue for the period, apply the rate, and compare with the output tax on the return. It will not match exactly — zero-rated supplies and timing differences see to that — but you should be able to explain every unit of the gap in one sentence. If you cannot, something is miscoded.

This period against last. Put the two returns side by side. Any line that has moved more than about 20% gets a reason written next to it before you file. Half the time the reason is real and interesting — a big order, a seasonal dip. The other half, it is an error you have just caught for free.

File, then write the note

File the return, pay, and keep the acknowledgement with the working papers rather than in an inbox.

Then spend ten minutes writing a note for next month: what took the longest, which records were missing, which supplier sends unusable invoices. That note is why our clients' third close takes four days when their first took three weeks. It is not that the work got easier. It is that each month removed one obstacle permanently.

What makes this fast or slow

The clients who file in an afternoon have three things in common, and none of them are accounting skills. Sales invoices can only be raised in one place. The bank is reconciled weekly, not monthly. And there is a named person who owns the file, so nothing waits on a question nobody is responsible for answering.

Get those three right and the return is clerical. Get them wrong and no amount of tax knowledge will save the deadline.