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How to Calculate Days Sales Outstanding for Your Agency

6 min read  ·  Agency cash flow

Your agency could be profitable on paper and still run out of cash. This happens more often than most agency owners expect, and one of the main culprits is a metric called Days Sales Outstanding — or DSO. It measures the gap between when you invoice a client and when you actually receive the money. That gap, multiplied across every client, is the silent drain on your cash flow.

Understanding DSO doesn't require an accounting background. It requires about five minutes and a copy of your accounts receivable balance.

The DSO formula

DSO tells you the average number of days it takes your agency to collect payment after invoicing. The calculation is:

Where "accounts receivable" is the total outstanding invoices at a given point in time, "revenue" is the revenue earned over a specific period, and "number of days" is the length of that period (typically 30 for monthly or 90 for quarterly).

For example: if your agency has £80,000 in outstanding invoices and earned £300,000 in revenue over the last 90 days, your DSO is (80,000 ÷ 300,000) × 90 = 24 days. That means on average, you're being paid 24 days after invoicing.

What good DSO looks like for agencies

DSO range	Assessment	What it usually means
Under 30 days	Healthy	Tight terms, good follow-through on invoices
30–45 days	Concerning	Slippage on terms, slow-paying clients building up
45–60 days	Dangerous	Cash gap emerging; growth will make this worse
60+ days	Critical	You are effectively financing your clients' operations

Most healthy digital agencies operate with a DSO between 20 and 35 days. Anything beyond 45 days deserves serious attention, not just because of the cash impact today, but because of what happens when the agency grows.

Why high DSO kills agencies — especially growing ones

The maths here is simple but brutal. Your agency pays salaries, software subscriptions, and overhead on a monthly cycle. Most of those costs land at the start of the month. But if your clients are paying 60 days after invoicing, you're covering 60 days of costs before the corresponding revenue arrives in your account.

At a small scale, this is manageable — uncomfortable, but manageable. As revenue grows, the problem scales with it. An agency billing £50k per month with 60-day DSO needs to float roughly £100k in receivables at any given time. If that agency doubles to £100k per month, the float becomes £200k. The agency needs more cash in the business just to sustain its growth, regardless of how profitable it is.

This is why agencies that appear to be thriving can suddenly find themselves unable to make payroll. Revenue is there. Profit is there. Cash is not — because it's sitting in unpaid invoices scattered across a dozen clients.

Common causes of high DSO at agencies

Vague or long payment terms. The most common cause. An invoice with 30-day payment terms sent at the end of the month won't be paid until the end of the following month. Add processing time at the client's accounts payable department, and you're looking at 45–60 days in practice. The fix starts with shorter terms — 14 days is entirely reasonable for agency work.

Not chasing overdue invoices. Many agency owners find invoice chasing uncomfortable, particularly when the client is a valued relationship. The result is that invoices sit unpaid for weeks or months past due, not because the client is unwilling to pay but because no one has asked them to. Automated payment reminders remove the awkwardness entirely.

Big clients using you as a bank. Enterprise clients often have procurement processes that mandate 60 or 90 day payment terms. They're not being difficult — it's just how their accounts payable works. The problem is that small agencies don't have the balance sheet to absorb those terms across multiple large clients. If you work with enterprise clients, factor DSO into your pricing — if they pay in 90 days, your effective rate needs to account for the cost of carrying that receivable.

No upfront payment structure. Sending a single invoice at the end of a project means you've done all the work before receiving any money. A 50% deposit upfront and 50% on completion not only improves DSO — it also reduces the risk of non-payment entirely, because a client who has already paid half is more invested in completing the project.

How to reduce your DSO

• Shorten payment terms to 14 days for all new contracts. For existing clients, renegotiate at contract renewal. Most won't push back.
• Require a 50% deposit on project work before starting. Frame it as standard practice — it is, for well-run agencies.
• Automate invoice reminders at 7 days before due, on the due date, and 3 days after. Most accounting software handles this. It removes the personal awkwardness and dramatically reduces late payment.
• Add late payment terms to your contracts. A 1.5% monthly interest charge on overdue invoices isn't just about the money — it signals that you take your terms seriously, which affects how quickly clients prioritise your invoices.
• Invoice immediately. Many agencies invoice at month end as a batch process. But a project completed on the 5th doesn't need to wait until the 31st to be invoiced. Send invoices within 24 hours of milestone completion.