VAT set-aside calculator

4 min read

Quarterly bill estimateWhat you'll owe

Weekly reserve figureWhat to save

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What this calculator does

VAT catches out more cash-healthy businesses than almost anything else, because the money you collect on sales feels like yours until the quarter ends and HMRC wants it. This calculator works out roughly what your quarterly VAT bill will be and, more usefully, the weekly amount to set aside so it's already waiting when the return falls due.

You enter your VATable sales and VATable purchases for the quarter and your VAT rate, and it returns the net VAT payable plus a per-week reserve figure. It's built for UK limited companies on standard VAT accounting who want to stop treating the quarterly bill as a nasty surprise and start funding it quietly, week by week.

How to use it

Use the figures for a typical quarter, net of VAT:

VATable sales — the value of standard-rated sales in the quarter, excluding the VAT itself. This is the VAT you charge customers (output tax).
VATable purchases — the value of standard-rated costs on which you can reclaim VAT (input tax): stock, equipment, services. Leave out wages, most insurance and anything VAT-exempt.
VAT rate — 20% standard for most goods and services; 5% reduced or 0% for certain items.

The result is your net VAT and the weekly amount to move into a separate pot. Setting it aside weekly, into a dedicated account you don't dip into, turns a daunting quarterly lump into thirteen painless transfers.

How to read the result

Two numbers matter. The net VAT payable is the VAT you've charged on sales minus the VAT you can reclaim on purchases — the cheque HMRC expects each quarter. The weekly reserve is that figure divided across the thirteen weeks of the quarter: the small, steady amount that, if you actually move it, means the bill is funded before it arrives.

The discipline is everything. The reason VAT bites is that the collected tax sits in your main account looking spendable, so it gets spent — on stock, wages, a quiet month — and then the return lands. Keeping the weekly reserve in a separate account removes the temptation entirely. If the bill is large and a quarter coincides with a seasonal dip, plan the bridge early rather than scrambling; a short-term facility can cover a one-off timing clash, but the cheaper fix is simply reserving as you go.

The formula in plain English

Standard VAT accounting nets off what you charge against what you reclaim:

Output VAT = VATable sales × VAT rate

Input VAT = VATable purchases × VAT rate

Net VAT payable = output VAT − input VAT

Weekly reserve = net VAT payable ÷ 13

So a business charging £20,000 of output VAT and reclaiming £6,000 of input VAT owes £14,000 for the quarter, which is about £1,077 to set aside each week. If your input VAT ever exceeds your output VAT — common after a big equipment purchase — the net figure is a refund rather than a bill, and there's nothing to reserve that quarter.

Worked example

A consultancy makes £60,000 of standard-rated sales in a quarter and has £10,000 of VATable costs, all at 20%.

Output VAT = £60,000 × 20% = £12,000. Input VAT = £10,000 × 20% = £2,000. Net VAT payable = £12,000 − £2,000 = £10,000. Weekly reserve = £10,000 ÷ 13 = about £770 a week. Move that into a separate VAT account every week and the £10,000 bill is fully funded the day the return is due — no scramble, no surprise, no need to borrow to cover it. Figures are illustrative.

Limitations to keep in mind

This estimates standard VAT accounting and assumes a typical quarter. It won't be exact if your sales are seasonal, if you're on the Flat Rate or Cash Accounting schemes, or if a big one-off purchase swings the input VAT. Use a representative quarter and round the weekly reserve up for safety — over-reserving simply leaves a small surplus, which is no bad thing.

It's a cash-discipline tool, not tax advice; your accountant or HMRC's guidance governs what's actually VATable and which scheme suits you. Pair the weekly reserve habit with the cash runway calculator so tax set-asides are built into your real burn, and the VAT calculator for one-off figures. This is general information, not financial or tax advice.

Frequently asked questions

Why do I owe VAT when it never felt like my money?

Because it never was. The VAT you charge customers is collected on HMRC's behalf — you're a tax collector, not the owner of that cash. It only feels like yours because it sits in your main account between returns. Setting it aside weekly into a separate pot keeps the distinction clear and the bill funded.

Should I really open a separate account for VAT?

It's one of the simplest, most effective cash-flow habits a business can adopt. Money out of sight in a dedicated VAT account doesn't get spent on stock or wages by accident, so the quarterly bill is already covered when it lands. The same trick works for Corporation Tax and PAYE.

What if a VAT bill clashes with a quiet trading month?

If you've been reserving weekly, the bill is funded regardless of how trade is going that month — that's the whole point. If a one-off clash still leaves a gap, plan a short-term bridge early rather than scrambling; a revolving facility can cover a timing mismatch, but reserving as you go is cheaper and avoids borrowing for tax at all.