How to build a simple cash flow forecast for your startup

A cash flow forecast shows the money you expect to come into and go out of your UK e-commerce business over the coming months. It helps you anticipate shortfalls, plan inventory purchases and avoid running out of cash even when sales are growing.

This guide walks you through building a simple 12-month projection using a spreadsheet. The process is designed for early-stage founders selling online in the UK, focusing on realistic timing of receipts and payments rather than accounting profit.

Why cash flow matters more than profit for e-commerce startups

Profit on paper can look healthy while your bank balance is dangerously low. This happens because sales on platforms like Shopify or Amazon may not be paid immediately, stock must be paid for upfront, and VAT is often due before you have collected it from customers.

A cash flow forecast tracks actual bank movements. It reveals when you might need to delay a supplier order, accelerate invoice chasing or arrange short-term funding. For UK e-commerce sellers this is especially important because of the fast turnover of inventory and the impact of platform fees and advertising costs that are paid in advance of sales.

Choose your tools and set up the spreadsheet

Use a spreadsheet such as Google Sheets or Microsoft Excel. Create a new file and label the columns for each of the next 12 months, plus a total column at the end. Add rows for every type of cash inflow and outflow you expect.

Keep the layout simple: one section for cash inflows, one for cash outflows, a row for net cash flow each month, and a running cash balance at the bottom. Colour code positive and negative figures for quick visual checks. Save a version each month so you can compare forecast against actual results.

Estimate your monthly sales receipts

Start with expected sales revenue. Break this down by product or channel if you sell on multiple platforms. For each month, estimate the number of orders and average order value, then multiply to get gross sales.

Adjust for payment timing. Sales made on your own website via Stripe or PayPal usually clear in 2–5 working days. Marketplace sales such as Amazon or eBay may take 14–30 days to reach your bank. If you offer credit terms to trade customers, add the expected delay. Enter only the cash you realistically expect to receive in each month, not the sale date. Be conservative; it is better to under-estimate receipts than to run out of cash unexpectedly.

List all cash outflows with realistic timing

Enter every payment you expect to make. Typical e-commerce outflows include:

• Cost of goods sold – when you actually pay suppliers, not when you sell the stock
• Platform fees and transaction charges – usually deducted at point of sale or paid monthly
• Online advertising and marketing costs – often paid in advance
• Packaging, postage and fulfilment – paid when orders are dispatched
• Salaries, National Insurance and pension contributions if you have employees
• Rent, utilities, software subscriptions and professional fees
• VAT payments to HMRC when due
• Corporation tax, self-assessment income tax or dividend payments when they fall

Research current rules on GOV.UK or HMRC for exact due dates as these change. Spread large one-off costs across the months they are likely to hit your bank account. Include a small buffer for unexpected repairs or returns.

Calculate net cash flow and closing balance

For each month, subtract total outflows from total inflows to show the net cash movement. Add this figure to the previous month’s closing balance to give the new closing balance. This running total is the most important number in the forecast.

If the balance goes negative, the forecast is telling you that you will need additional cash before that month. You can then explore options such as increasing sales, reducing stock orders, negotiating longer supplier terms or seeking finance. Update the spreadsheet each month with actual bank figures so the forecast stays relevant.

Refine the forecast with e-commerce specifics

Include seasonal patterns common in UK online retail such as higher sales in Q4. Factor in the timing of major advertising campaigns and the lag before they generate revenue. Account for refund rates by reducing expected receipts slightly or adding a separate refunds row.

Review supplier payment terms carefully. Some UK wholesalers require payment on order while others offer 30-day terms. Test different scenarios by copying the sheet and changing the sales growth or cost assumptions. This helps you understand which variables have the biggest impact on your cash position.

Review, update and use the forecast

Revisit the cash flow forecast at the start of each month. Replace estimates with actual bank transactions and adjust future months accordingly. Over time you will improve the accuracy of your predictions.

Use the document when speaking with potential mentors, accountants or funders. It demonstrates that you understand the cash dynamics of your e-commerce business. Free workspaces such as Loomworks in West Yorkshire can provide additional operator mentoring to help interpret and act on these figures.

Frequently asked questions

Related reading: How to price products to achieve healthy profit margins, How to register as an employer with HMRC and set up PAYE, What bookkeeping system should UK ecommerce sellers use?. Browse all tax & finance guides or apply to Loomworks.