Days sales outstanding: the number that tells you how you are really paid

Days sales outstanding is the average number of days between invoicing and being paid. It compresses your whole receivables position into one number you can watch over time, compare with your payment terms, and act on. For a business whose cash is tied up in unpaid invoices, it is usually more informative than revenue.

The calculation is simple: divide receivables by credit sales for the period, then multiply by the number of days in the period. A month with receivables of 90,000 and sales of 120,000 gives 90,000 ÷ 120,000 × 30, which is 22.5 days. The difficulty is not the arithmetic — it is reading the result honestly.

Calculating it without fooling yourself

• Use credit sales only. Including cash sales, which are paid immediately, flatters the figure and makes the trend meaningless.
• Use the same period length consistently — monthly is right for most small businesses, and quarterly hides too much.
• Use average receivables over the period rather than the closing balance when sales are lumpy, because a large invoice raised on the last day distorts the closing figure.
• Exclude amounts formally in dispute, and track those separately. They are a different problem with a different fix.
• Decide once whether the figure is gross or net of sales tax, and never mix the two — the difference can be a fifth of the number.
• Compare it against your stated payment terms. DSO of 45 on 30-day terms means 15 days of slippage; DSO of 45 on 45-day terms means the terms are the problem.
• Keep the ageing profile beside it, because the same DSO can describe a healthy ledger or one with a few very old debts.

DSO is an average, and averages hide concentration. One large customer paying at 90 days while everyone else pays at 20 can produce a comfortable-looking figure that describes nobody. Always read it alongside the ageing profile and the share of the balance held by your largest customer.

Building the tracker

1. One row per month with four columns: credit sales, opening receivables, closing receivables, and disputed amounts excluded.
2. Calculate average receivables as opening plus closing divided by two, then DSO as average receivables ÷ credit sales × days in month.
3. Add your standard terms as a constant column, and a slippage column showing DSO minus terms. Slippage is the number that is actually actionable.
4. Chart twelve months. The trend is the signal; a single month tells you almost nothing, especially where sales are seasonal.
5. Add an ageing summary beside it — current, 30, 60, 90+ as percentages of the balance — so concentration is visible.
6. Flag any customer above a share of the total you decide in advance. Concentration risk deserves a name, not a footnote.
7. Review monthly with the receivables list open, and record what changed rather than only what the number was.

What to do when it rises

A rising DSO has a small number of causes, and it is worth identifying which before acting. Invoicing later than you used to moves the whole curve, and it is the most common cause in a busy period. A shift in customer mix — larger customers with longer internal processes — raises it structurally, and the answer is different terms rather than harder chasing. A genuine deterioration in collections shows up as growth in the 60- and 90-day buckets rather than a uniform shift. And a single large late invoice can move the figure on its own, which is why you look at the ageing profile first.

Ettex Sheets is a comfortable home for the tracker: import an existing XLSX with formulas intact, 150+ functions with instant recalculation, conditional formatting to flag a month where slippage exceeds your threshold, charts from any range for the twelve-month trend, and pivots when you want DSO by customer or by segment. Cell comments with threads let a bookkeeper query a figure against the cell it lives in, and version history means last quarter's numbers are still recoverable. The invoice data behind it — amounts, due dates and statuses from draft through paid — comes from Ettex Invoices, and the ledger sits in Ettex Books.

Said plainly: Ettex does not calculate DSO for you. There is no receivables dashboard, no automatic ageing report, and no metric that updates as invoices are paid. You export the invoice data and maintain the tracker yourself. For a monthly review that is a ten-minute job; if you want a live figure on a dashboard, that is a different class of product.

Days sales outstanding is one number that answers a question everyone in the business is guessing at. Use credit sales only, track it monthly against your terms, and always read it beside the ageing profile.