Measure

Days Sales Outstanding (DSO)

The average number of days between invoicing and being paid. The headline measure of how well the back of the chain works — and one that moves for reasons that have nothing to do with collections.

Also called: Debtor days · Average collection period · Receivable days

Formula

DSO = (accounts receivable ÷ credit sales for the period) × days in the period

Unit: Days
Direction: Lower is better
How often: Monthly, read as a rolling trend. A single month in isolation is noise.
Normally owned by: Credit Controller

What it is

DSO expresses your receivables balance as a number of days of sales. If DSO is 62, then on average the business is waiting 62 days from invoice to cash — and is financing that period out of its own pocket.

It matters because receivables are usually one of the largest assets on a trading company's balance sheet and the one most directly convertible into cash. Reducing DSO by five days on a £20m business releases roughly £274,000 permanently, without selling anything more.

Its weakness is that it is a ratio of a balance to a flow, so it moves whenever either moves. A strong sales month raises the receivables balance and pushes DSO up, making collections look worse in a month where nothing about collections changed. That is why DSO should be read as a trend alongside the ageing profile, never as a monthly verdict.

What each term means

Accounts receivable: The outstanding receivables balance at the end of the period, net of credit notes. Exclude anything not genuinely collectable.
Credit sales: Sales invoiced on credit terms in the period. Cash sales do not create receivables and should be excluded.
Days in the period: The number of days the sales figure covers — 30 or 31 for a month, 365 for a year.

Calculating DSO, and then finding what it hides

Worked through with real numbers.

Inputs

Receivables at 30 June: £1,486,000
Credit sales in June: £742,000
Days in June: 30
Standard payment terms: 60 days from end of month

Calculation

DSO = (£1,486,000 ÷ £742,000) × 30
DSO = 2.003 × 30
DSO = 60.1 days
Terms of 60 days from end of month average about 75 days from invoice date,
so the effective standard is roughly 75 days, not 60.
Performance against terms = 60.1 − 75 = 14.9 days better than terms.

Result
60.1 days — which is about 15 days better than the payment terms actually allow.

How to read it
Read naively, 60 days looks poor. Read against the terms the business itself granted, customers are paying materially early. The problem this company has is not collections; it is that it agreed 60-day end-of-month terms, which is a commercial decision made at quotation stage and worth roughly £370,000 of permanently tied-up cash. Chasing harder cannot fix that. Only changing what is agreed at the front of the chain can.

How to decide what good looks like

We do not publish benchmark figures we cannot source, because the ones in circulation compare businesses using incompatible definitions. This is the method instead.

Do not start from an industry figure. Start from your own payment terms, because that is the number your DSO can legitimately be compared to.

Convert your standard terms into actual days from invoice date. 30 days net is 30. 60 days from end of month averages about 75. 'End of month following' is longer still. Weight by revenue where different customers have different terms.

The gap between your DSO and that weighted average is your collection performance — the only part of the number credit control controls. Anything beyond it is a commercial decision made at quotation, not a collections failure.

Set the target on that gap rather than on DSO itself. 'Within five days of terms' is a target a collections function can own; 'DSO of 45' may be arithmetically impossible given the terms the business has already agreed.

Track the trend over at least twelve rolling months. Because DSO moves with sales volume, month-on-month comparison mostly measures the sales pattern.

If an external comparison is wanted, published receivable days for listed companies in your sector can be derived from their filed accounts. Treat them as context, not a target — their customer mix, terms and sales pattern are not yours.

Where it misleads

PitfallTreating DSO as a pure measure of collections
Why it happens: It is the number finance reports and the one credit control is judged on.
What to do instead: Split it. The portion explained by agreed payment terms belongs to sales and commercial; only the excess over terms belongs to collections.
PitfallComparing months without accounting for sales volume
Why it happens: DSO is a balance divided by a flow, so a strong sales month inflates it and a weak one flattens it.
What to do instead: Use a rolling twelve-month view, or the countback method which matches the receivable balance against actual recent sales rather than an average.
PitfallIncluding uncollectable debt in the balance
Why it happens: Removing it requires a write-off decision nobody wants to take.
What to do instead: Provide for or write off genuinely dead debt. Carrying it makes DSO worse every month and tells you nothing new after the first.
PitfallIgnoring the invoicing lag
Why it happens: DSO starts at the invoice date, so days lost between despatch and invoice are invisible to it entirely.
What to do instead: Measure despatch-to-invoice separately. A three-day billing lag is real tied-up cash that DSO will never show.
PitfallUsing it as the only receivables measure
Why it happens: It is a single number and it fits on a dashboard.
What to do instead: Read it with the ageing profile, the value of invoices in query, the percentage paid within terms and unallocated cash. DSO says something is wrong; the others say what.
PitfallExcluding credit notes from the calculation
Why it happens: They sit in a different part of the ledger and are easy to overlook.
What to do instead: Net them off. A large unapplied credit balance flatters DSO while hiding a real dispute.

How it gets gamed

Rarely dishonestly. Mostly these are things a reasonable person does when a number becomes a target.

Pushing invoicing into the following period so the receivable never appears in this one's balance.
Factoring or discounting receivables, which converts them to cash and cuts DSO without changing customer behaviour.
Writing off aged debt at period end purely to improve the ratio.
Offering settlement discounts that cost far more than the financing they save.
Selectively excluding a problem customer as 'non-standard' in the reported figure.

Where it fits

Measured at these steps

Read alongside

Gross Margin

Common questions

›What is a good DSO?

The only defensible answer is: close to the payment terms you actually agreed, adjusted for how those terms convert into real days. A DSO of 62 on 30-day terms is poor; the same 62 on 60-day end-of-month terms is good. Any figure quoted as a universal benchmark ignores the one variable that determines it.

›Why did DSO get worse when collections improved?

Almost always because sales rose. DSO divides a receivables balance by recent sales, so a strong month inflates the balance before the cash has had time to arrive. This is the single most common misreading of the measure, and it is why the rolling trend matters more than the monthly figure.

›What is the countback method?

An alternative calculation that works backwards through recent months' sales, consuming the receivable balance month by month, to find how many days of actual sales the balance represents. It is more resilient to uneven sales patterns than the simple formula and is worth using where monthly revenue is lumpy.

›Does DSO include disputed invoices?

It should, because they are still uncollected cash — but they should also be reported separately. An invoice in query is not a collections failure in the same sense as one simply unpaid, and the fix belongs to a different department. Blending them together conceals which problem you have.

›How much is a day of DSO worth?

Annual credit sales ÷ 365. On a £20m business, one day is roughly £54,800 of cash permanently tied up, so five days is £274,000. That figure is worth calculating once and quoting internally, because it converts an abstract ratio into a number people act on.

›Should DSO be a collections target?

Not directly, because most of it is determined by terms the collections function did not negotiate. Target the gap between DSO and weighted average terms instead. It is the part that can actually be influenced, and it does not punish a team for a commercial decision made months earlier at quotation stage.

Tools that calculate this

They do the arithmetic and show the workings. If you only want the method, everything you need is on this page.

Reviewed 2026-08-15. The formulas behind every CapsuleM8 tool are published in the methods reference.