Debtor Days for Small Businesses: The Monthly 20-Minute Review

The number that prices your patience — the formula, what each extra day actually costs, the six numbers to pull every month, and the two levers that move it.

Most small businesses know their revenue to the dollar and have no idea how long their money takes to come home. Debtor days is the bridge between the two: the average number of days between sending an invoice and getting paid. It is the single number that decides whether growth is a gift or a trap — a business that invoices $96,000 a month and waits 58 days for payment is permanently funding about seven weeks of someone else's payroll, and every new customer makes that loan bigger. This page is the monthly review that keeps the number visible and moving down: fifteen minutes of pulling numbers, five minutes of deciding. The overdue invoice letters handle the individual invoice that is already late; this review watches the fleet.

1. The formula — and what a day is actually worth

The arithmetic is one line, run on the same day every month so the months compare:

Debtor days = (accounts receivable ÷ total credit sales) × days in the period.

Pull receivables from the balance sheet on the last day of the month, credit sales from the same month's invoicing (cash sales excluded — they never wait), and use the month's actual day count. A business holding $186,000 of receivables against $96,000 of monthly invoicing is at 186 ÷ 96 × 30 ≈ 58 days. The number only means something against two comparisons: last month (trend) and your own invoice terms (promise vs. reality — if terms are net-14 and the number is 58, customers are paying four times later than agreed, and that is a decision someone is making, not weather).

What a day is worth: one debtor day on that business equals about $3,200 of cash sitting in customers' bank accounts instead of yours — a month's worth of sales divided by thirty. Ten days trimmed from the number is a month of payroll funded from receivables instead of the overdraft, which is exactly where the cash runway checklist gets its months-of-cover from.

2. The monthly 20-minute review — six numbers, five decisions

Same calendar day each month (the first working day after the month-end close), same person, twenty minutes:

• Receivables balance — the total owed to you on the last day of the month.
• Credit sales for the month — invoiced, not banked.
• The ratio — the one line of arithmetic above; write it down next to last month's.
• The aged breakdown — receivables split into current / 1–30 days late / 31–60 / 60-plus. The total can look stable while the 60-plus bucket quietly doubles; the buckets are where the queue hides.
• Largest three balances — name them. Concentration is a second risk hiding inside the first: if one customer is 40% of receivables, your payment schedule is one accounts-payable clerk's mood.
• Days-to-invoice — average days between doing the work and sending the invoice. This number is yours alone, costs nothing to fix, and is the most common reason a good payer looks bad.

Five minutes of decisions: any 60-plus bucket growing? escalate those names up the overdue ladder one step today. Largest-three concentration above a third of receivables? cap or deposit the next job with that customer. Days-to-invoice above three? that is this month's fix, not the customers'. Terms mismatch (net-14 promised, 58 measured)? the problem is the chasing cadence, not the customers. Number moved the wrong way two months running? change one lever, not five.

3. The two levers — and the third that comes free

• Lever one: invoice the same day the work is done. Days-to-invoice is pure margin on the number, owned entirely by the business. Work finished Tuesday and invoiced the following Monday has already burned five days nobody negotiated for. The fix is mechanical: invoice trigger attached to job completion (the cleaner's run sheet closes with the invoice sent; the trade's van leaves when the invoice leaves), same-day, every job. On 58 debtor days with a 5-day invoicing lag, sending same-day is worth roughly 8% of the receivables balance immediately — before a single customer changes behaviour.
• Lever two: chase on a schedule, not on a mood. The business that chases when cash feels tight trains customers to pay the businesses that chase on schedule first. The cadence is written, not improvised: reminder at day 7 after due, the polite-but-specific step at day 14, the formal step at day 30 — the three-letter ladder exists precisely so the chase is a process. Automated reminders where the software has them; a named ten-minute slot in the calendar where it doesn't.
• The third lever comes free with new customers: terms are set at onboarding and never renegotiated under pressure — deposits on first jobs, short terms for strangers, as in the terms that stop the next late payer. Every new customer at net-14 instead of net-60 is a permanent ten-day improvement in the average; the supplier side of the same coin is the supplier payment terms checklist, because the spread between when money leaves and when it arrives is the actual number your bank cares about.

4. The four traps

• Watching the total, not the buckets. A receivables total that grows with revenue looks healthy; the 60-plus bucket inside it can double while the ratio barely moves. The aged breakdown is the review; the total is the summary.
• The growth illusion. Sales up 20% with debtor days flat means receivables up 20% — growth on terms you fund yourself. The number to watch alongside sales growth is always the ratio, because that is what the extra growth is financing.
• Blaming the customer for the invoicing lag. Days-to-invoice of nine makes even a 30-day payer look like 39. Split the number into the part you own and the part they own before the first difficult phone call — half the "bad payers" are a lagging invoice queue.
• Fixing the number once and never again. A one-off clean-up after a scary quarter decays; chasing drifts back to mood, invoicing drifts back to "Friday if there's time." The review is twenty minutes a month, forever, in the same sitting as the month-end close — the number only stays down when it stays watched.

Worked example: the commercial cleaning company and the 58

A commercial cleaning company with $96,000 of monthly invoicing ran its first review and found the receivables at $186,000 — 58 debtor days on net-14 terms, meaning customers paid on average four times later than the invoice promised. The aged breakdown made it concrete: $9,400 in the 60-plus bucket, and the largest three balances (a shopping-centre contract, a gyms group, a state government contract) made up 41% of everything owed. The fix took one month and no difficult conversations: invoicing moved to same-day (the average lag had been 6 days — the supervisors' run sheets were simply closed with "invoices sent" as the last line); the day-7 reminder went automated; the three large balances got the day-14 letter, by name, once; and the two new contracts signed that quarter went on net-14 with a 30% deposit instead of the informal "we'll sort payment monthly" the old ones had. By the next review receivables were $108,000 — 34 days. The $78,000 difference funded the company's own payroll through a soft December without touching the overdraft, and the shopping-centre contract — the 60-plus offender — paid every month since, because the account manager finally had a schedule to run instead of a mood. The owner's summary: "We weren't being stiffed. We were just the last company on their list, every month, by default."

From the HIVE80lab kit

Every page ships with a kit block — the paid tools behind the free advice:

• The First 30 Minutes — free incident quick-start checklist
• Ops Starter Kit — incident response for small teams — $14
• Ops Starter Kit Vol. 2 — advanced incident response & communications — $27
• Ops Mega Bundle — all 5 kits in one download — $49

Related: the overdue invoice letters are the three-letter ladder this review feeds names into; the supplier payment terms checklist is the paying side of the same spread — the gap between the two sides is your actual cash position; the cash runway checklist is what the recovered days are worth in months of cover; and the month-end close is where this twenty minutes lives on the calendar.

Related: the debtor-days number is the truth; the 13-week cash flow forecast is the calendar it feeds — each customer's real payment behaviour, week by week, is where your cash actually lands.

Related: the budget vs actuals review and the debtor-days review are the same ritual pointed at different lines — one reads the plan against the books, the other reads the clock against the receivables.

Related: gross margin by job is the pricing-side sibling of this review — debtor days prices your patience, the gross margin pricing review prices the work itself; a thin-margin job and a slow-paying job are both quotes you made without a floor.