For many of the businesses we work with, sales can look healthy on paper, but the cashflow tells a different story. We often find that millions of pounds are sitting in unpaid invoices. Whilst at the same time, suppliers, staff and lenders still need (and expect) to be paid on time. Glen Morgan, who leads itsettled and has spent nearly three decades working in credit management, sees this pattern regularly across UK mid-market businesses: millions of pounds sitting in aged debt that could be working capital. Understanding and monitoring your debtor days is one of the most effective ways to diagnose the problem early. This guide explains how to calculate debtor days, how to interpret the result, and critically what to do if the figure is too high.
Contents
- What are debtor days?
- Why debtor days matter
- The debtor days formula
- How to calculate debtor days step-by-step
- Debtor days calculation example
- What is a good debtor days figure?
- Debtor days by sector: UK benchmarks
- Common mistakes when calculating debtor days
- How to reduce debtor days
- Frequently Asked Questions
What are debtor days?
Also known as Days Sales Outstanding (DSO), debtor days measure the average number of days it takes customers to pay their invoices. Simply put: the lower the figure, the faster cash flows into the business. The metric compares outstanding accounts receivable (your sales ledger) against annual credit sales and converts the result into an equivalent number of days. For example, if your payment terms are 30 days but your debtor days figure sits at 65, customers are on average taking more than twice as long as expected to settle invoices. Debtor days are typically monitored alongside cashflow forecasts, aged debt reports and working capital performance, because together they give a clear picture of how effectively receivables are being managed.
When the debtor days figure is high, it is often a warning sign of collection issues, customer payment problems, or weaknesses in credit control processes.
Why debtor days matter
There are several reasons why finance leaders should monitor debtor days closely:
- Improving cashflow visibility
- Identifying collection issues early
- Reducing reliance on borrowing or invoice finance
- Strengthening working capital
- Supporting more accurate forecasting
- Improving relationships with funders and stakeholders
- Reducing the risk of bad debt
Late payments remain a significant challenge for UK businesses, costing the economy an estimated £11 billion per year. Finance teams end up spending valuable time managing overdue accounts instead of focusing on strategic priorities – and the longer invoices remain unpaid, the greater the risk they become unrecoverable.
The debtor days formula
The standard debtor days formula is:
Debtor Days = (Total Sales ledger value, net of vat ÷ total annual sales) × number of days 365.
The result shows the average number of days customers take to pay.
How to calculate debtor days
Step 1: Find your debtors’ balance
Look at your aged debtor report.
Divide by 1.2 to remove vat
For example:
Debtors = £1,800,000 – (£1,500,000 when divided by 1.2)
Step 2: Identify annual sales figure
Calculate your total credit sales for the last 12 months. Use credit sales only — not total revenue — to avoid distorting the result (see Common Mistakes below).
Example: Annual credit sales = £6,000,000
Step 3: Apply the formula
Using the figures above:
Debtor Days = (£1,500,000 ÷ £6,000,000) × 365
Debtor Days = 0.25 × 365
Debtor Days = 91.25 days
Your debtor days figure is 91 days.
This means customers take an average of 91 days to pay their invoices.
For businesses with significant sales volumes, even a reduction of 10 days can release substantial amounts of working capital back into the business.
In this example 10 days is £164k of extra cash.
What is a good debtor day figure?
There is no single ‘perfect’ figure – it depends on your industry, customer base and payment terms. However, UK mid-market businesses typically report debtor days of between 40 and 60 days, which means many are already running above their stated payment terms. As a general guide:
| Debtor days | What it usually shows | UK mid-market context |
| Under 30 days | Excellent collections performance | Uncommon in mid-market; indicates very tight credit control |
| 30–45 days | Healthy and manageable | Typical for businesses with 30-day terms and strong processes |
| 45–60 days | Worth monitoring closely | Close to the UK mid-market average; review collections cadence |
| 60–90 days | Potential cashflow concern | Above average; investigate aged debt and collections gaps |
| Over 90 days | Significant collection issues | Well above the UK average; specialist support likely needed |
The most useful benchmark is your own payment terms. If your standard terms are 30 days but debtor days are consistently above 60, there is likely a gap in your collections process that is costing you working capital. Many mid-market businesses find that debtor days creep upward over time due to unresolved invoice disputes, inconsistent follow-up, insufficient resource, or the absence of a formal credit policy.
Debtor days by sector: UK benchmarks
Debtor days vary significantly by sector, which is why it’s important to compare your figure against relevant peers, not just a generic average. As a rough guide for UK mid-market businesses:
- Manufacturing: typically 55 – 70 days. Extended supply chains and B2B payment cycles mean longer terms are common, but anything above 75 days warrants review.
- Recruitment: typically 45-60 days. Thin margins make cash velocity critical; high debtor days in this sector can quickly create liquidity pressure.
- Professional services: typically 50-65 days. Disputes over deliverables and scope are a common driver of late payment.
- Construction: typically 65-80 days. Retention payments and lengthy payment chains mean this sector routinely operates with higher debtor days than most.
- Wholesale and distribution: typically 40–55 days. Volume relationships with major buyers can distort the average significantly.
Source: Shuttle DSO Benchmarks 2026
If your debtor days are materially above the typical range for your sector, it is worth investigating whether the issue lies in collections process, customer concentration, or dispute management.
Common mistakes when calculating debtor days
- Using total revenue instead of credit sales – this can distort the result.
- Using outdated debtor balances – always use the most recent accounts receivable figure available.
- Looking at one month in isolation – trends over time are more valuable to analyse.
- Ignoring aged debt – for a complete picture review debtor days alongside aged debt.
How to reduce debtor days
If your debtor days are increasing or consistently above your payment terms, there are several practical steps to take.
- Strengthen your credit control procedures
A formal collections process with clear ownership, escalation paths and consistent follow-up schedules makes a significant difference. Without documented procedures, collections activity becomes reactive and inconsistent — and debtor days drift upward as a result.
- Invoice promptly
Delays in issuing invoices directly delay payment. If invoices go out days after work is delivered, the payment clock starts late — and so does your cashflow.
- Resolve disputes quickly
Customer disputes are one of the most common causes of overdue invoices. Establishing a clear dispute resolution process — with defined response times and ownership — prevents individual accounts from stalling your entire debtor days figure.
- Monitor aged debt regularly
Weekly aged debt reviews help identify accounts that need attention before they become serious collection problems. The earlier an issue is flagged, the more options you have for resolution.
- Communicate earlier
The most effective collections strategies begin before invoices become overdue. Proactive reminders and pre-due communications reduce the number of accounts that slip into arrears in the first place.
- Review customer credit limits
Regular credit reviews reduce exposure to higher-risk accounts. As customer circumstances change, credit limits and payment terms should be reviewed accordingly.
- Consider specialist support
Where debtor days have become significantly elevated above payment terms, or where internal resource is stretched, businesses often benefit from bringing in specialist receivables management support. This can help recover overdue debt, rebuild credit control processes and deliver lasting improvements without disrupting customer relationships. See our guide on what to look for in a credit management partner for a checklist of what to consider.
Next steps
Calculating debtor days is one of the simplest and most effective ways to measure the health of your cashflow. Tracked regularly, it allows business leaders to identify collection issues early, improve working capital, reduce funding pressures and make more informed decisions about credit exposure. If your debtor days are consistently above your payment terms — or rising quarter on quarter — it is worth taking a structured look at where the gaps are.
Our free Working Capital Healthcheck is a good starting point: it benchmarks your cashflow position and identifies where the biggest opportunities for improvement lie.
If you’d prefer to talk it through directly, get in touch with the itsettled team — a short conversation is usually enough to give you a clear picture of where things stand and what a realistic improvement looks like.
FAQs
What is the difference between debtor days and DSO?
Nothing – they are different names for the same metric. Debtor days is the term more commonly used in the UK. Both are calculated using the same formula and measure the same thing: the average number of days customers take to pay.
How often should I calculate debtor days?
Most businesses calculate debtor days monthly as part of their management accounts. Finance teams under cashflow pressure, or businesses with high invoice volumes, may benefit from monitoring it weekly to catch deterioration early.
What causes high debtor days?
The most common causes include late or inaccurate invoicing, unresolved customer disputes, poor collections follow-up, understaffed credit control functions, the absence of a formal credit policy, and customers experiencing financial difficulty. In many cases, it is a combination of process gaps and resourcing rather than a single root cause.
Can debtor days affect cashflow?
Yes, directly. Higher debtor days mean cash remains tied up in unpaid invoices for longer. For a business with £6m in annual credit sales, reducing debtor days from 65 to 45 releases approximately £329,000 in working capital — cash that was always owed but simply wasn’t moving fast enough through the business.
Is a high debtor days figure always bad?
Not necessarily. Some industries operate with longer payment cycles by convention, and large customer relationships can distort the average. However, debtor days should always be assessed against your agreed payment terms and your own historical performance. If the figure is rising over time, that trend matters more than the absolute number.
What is the quickest way to reduce debtor days?
The fastest improvements typically come from proactive collections activity starting before invoices are due, rapid resolution of invoice disputes, and consistent credit control follow-up. Structural improvements — credit policies, process documentation, team capability — deliver more durable results over the medium term.
Should I monitor debtor days or aged debt?
Both. Debtor days gives you a headline performance measure that tracks over time. Your aged debt report shows where the problems are concentrated — which specific accounts, and how long they have been outstanding. Used together, they give a complete picture of your receivables position.