Cash Flow Calculator for UK Businesses

Last reviewed: 17 May 2026

Project 12-month UK business cash flow in sterling with HMRC VAT-quarter awareness. Highlights months with negative balances and runway risk.

Cash flow is monthly income minus monthly expenses, tracked as a running balance from opening cash. A 12-month projection plots that running balance month by month and flags any month it goes negative. Most cash crises are visible 3–6 months in advance if you project regularly.

A 12-month UK cash flow forecast tracks monthly cash in (sales, VAT refunds, grants) and cash out (payroll, VAT, PAYE, Corporation Tax, suppliers, rent) to project bank balance. Two UK timing traps catch SMEs: quarterly VAT due one month and seven days after quarter-end, and the 31 January self-assessment payment-on-account.

Cash flow is where profitable UK businesses go to die. You can run a 15% net-margin business into administration in twelve months if customer payment terms are 60 days, suppliers want 30, and you've just hit an £18,000 VAT bill the same week as payroll. P&L solvency and cash solvency are different problems, and this 12-month forecast tool models the cash side.

UK cash flow inputs that catch people off-guard:

VAT returns — typically quarterly to HMRC, due one calendar month and seven days after the period ends, with electronic payment by direct debit. Plan for a single month's VAT liability as a cash outflow
PAYE / NI — monthly to HMRC, due 22nd of the following month if paying electronically (19th for cheques)
Corporation Tax — due 9 months and 1 day after the company's year-end (or quarterly instalments if profits over £1.5M)
Self-assessment payments on account — for sole traders and personal returns: 31 January (balancing + first instalment) and 31 July (second instalment), each typically half the previous year's tax bill
VAT registration — mandatory at £90,000 rolling 12-month turnover (2024 threshold). Crossing the line mid-year is a common cash shock if you haven't priced VAT-inclusively

The calculator builds out the next 12 months row-by-row: - Cash in: sales × collection timing (this month, +30 days, +60 days, etc.) - Cash out: payroll, suppliers, rent, software, VAT (every 3 months), PAYE (monthly), Corporation Tax (annually), other - Opening balance → closing balance for each month - Flags: any month where projected closing balance goes negative

For UK SMEs, the British Business Bank's cash flow templates and HMRC's payment deadlines on gov.uk are the authoritative references. If the forecast shows a negative month, the order of remedies is: tighten receivables (invoice day 1, chase day 7, escalate day 21), extend payables, pull forward sales, then financing.

Worked example

UK SME example — spotting the VAT-quarter dip.

A consultancy opens the year with £15,000 cash. Most months bring in £20,000 and spend £17,000 — a £3,000 monthly surplus. But in April a £12,000 quarterly VAT bill and the monthly PAYE both land, pushing that month's expenses to £30,000.

Typical month net: 20,000 − 17,000 = +£3,000.
April net: 20,000 − 30,000 = −£10,000.
Running balance before April climbs from £15,000 toward £24,000; April then drops it to about £14,000.

The annual net cash flow stays clearly positive, yet the tool's lowest-balance flag pinpoints April as the squeeze. Because cash never turns negative here, no financing is needed — but had opening cash been £6,000, April would breach zero, and the owner would tighten receivables one quarter ahead rather than scramble in the VAT week.

See the formula

See parent calculator at /cash-flow-calculator for the full formula reference.

Frequently Asked Questions

How do I enter quarterly VAT in a tool with monthly rows?

Add the VAT payment to the Expenses cell of the single month it leaves your account — one calendar month and seven days after each quarter-end. Don't spread it across three months; UK VAT is a lumpy outflow, and smoothing it hides exactly the cash dip the forecast exists to reveal. The calculator then flags whether that month's running balance survives the hit.

Should income go in the month I invoice or the month I'm paid?

The month cash actually arrives. The projection tracks bank balance, not accruals, so a January invoice on net-30 terms belongs in the February income cell. Entering sales in the month they were made — the most common cash-flow mistake — makes the forecast look healthier than reality. Add a buffer too: 15-20% of invoices typically slip past their due date.

Where do PAYE, Corporation Tax, and self-assessment payments go?

All in the Expenses cell of the month each is due. PAYE/NI is monthly, payable by the 22nd of the following month electronically. Corporation Tax is due 9 months and 1 day after year-end. Sole-trader payments on account fall on 31 January and 31 July. Placing each in its correct month is what turns a flat forecast into one that exposes the real tax-driven dips.

The forecast shows a negative month — what's the order of remedies?

Work cheapest first. Tighten receivables (invoice day one, chase day seven, escalate day twenty-one), then extend payables, then pull sales forward, and only then arrange financing. The calculator highlights the lowest-balance month so you can act before it arrives — arranging an overdraft three months ahead is far cheaper than scrambling for emergency cash the week it bites.

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Methodology & sources

Rates last verified: May 2026

Read the full methodology →

Standard cash-flow projection: running balance = opening cash + cumulative (income − expenses). Inputs are estimates; actual cash flow depends on timing of customer payments and supplier terms.

Rates are reviewed annually or when a region changes its headline rate. If you spot one that's out of date, email [email protected].

For information only. This calculator does not constitute financial, accounting, or tax advice. Consult a qualified professional before making business decisions.

Try these scenarios

Pre-filled examples — click any chip to load the inputs and result.

How to project 12-month cash flow

Enter your opening cash balanceBank + liquid assets at the start of month 1.
Fill in each month's incomeEstimated revenue or cash receipts for each of the 12 months ahead.
Fill in each month's expensesEstimated total cash outflows — salaries, rent, software, supplier payments.
Read net cash flow and running balanceEach month shows net flow (green positive, red negative) and the running balance. The chart highlights any month where cash goes negative.

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Written by

James Blanckenberg

Founder, BusCalcTools

Founder of BusCalcTools and FinnCalc. Builds practical financial calculators for small business owners and freelancers across the US, UK, and South Africa.

Editorial review by: James Blanckenberg, Founder & Editor

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