Late invoice payments and cash flow: a worked example for SMBs

Search interest in “late invoice payments and cash flow” is usually a founder or finance person who already feels the line of credit and wants a language to explain the pressure without drama. The honest way to do that is: map days sales outstanding to working capital, show assumptions, and separate “slow AP” from “we are undercapitalized for our growth plan.” The article is not a substitute for an accountant, but a plain-language path from invoice dates to a conversation your bank or investors can follow.

Definitions: DSO, working capital, and what “late” is not

Days sales outstanding, roughly, is the average time between issuing an invoice and getting paid, under whatever definition you use. Working capital, roughly, is the short-term money needed to run operations: receivables plus inventory-style funding minus payables. “Late” in human language is not always the same as “overdue in your system” if your customer and you disagree on a deliverable, so treat disputes as a state, not a day count.

Hypothetical table (simplified; plug your own numbers with your bookkeeper)

Suppose annual revenue in year one is 1,200,000, all on credit, and for simplicity the average open receivable balance is 100,000. If, over the year, your average DSO is 30 days, you are, very roughly, carrying about one month of sales in the pipe at any one time, subject to your mix and your definition of the invoice start date. If DSO drifts to 40 days, with the same business model, the average balance might scale roughly 33% higher, meaning more bank line or more cash on hand, before you have spent a pound on a new machine or hire. The numbers are for intuition; your ledger rules win.

The AR levers that move DSO in the real world

• Terms you can enforce without debate (written, consistent).
• Pre-due reminders that help AP schedule a batch, not a generic nag.
• Clear dispute handling so a scope fight does not sit in “open receivable” limbo for 90 days for lack of a human decision.
• A promise log so a customer who said “20th” does not get a robot email on the 18th that ignores the promise.

When the solution is not “send more email”

If you are out of covenant because growth outran cash, the fix may be a facility or equity conversation, not a 10% improvement in dunning. If you are in covenant and still stressed, a few days of DSO might be enough to buy breathing room, which is when automation and a schedule matter. The unpaid invoice impact article covers human and operational drag; this one stays focused on the money calendar.