Best possible DSO explained: formula and benchmark

Best possible DSO is the lowest days sales outstanding a company could reach if every customer paid exactly on terms and nothing went overdue. You calculate it using only your current, not-yet-due receivables instead of your total balance. It sets a realistic floor for collection speed, and the distance between it and your actual DSO is the cash your collections process can still win back.

Where standard DSO tells you how fast you collect, best possible DSO tells you how fast you could collect if overdue balances disappeared. That makes it the more honest target. It strips out the part of DSO that is baked into your payment terms and leaves only the part you control.

What is best possible DSO

Think of your receivables in two piles: invoices that are still inside their terms (current) and invoices that have aged past due (overdue). Standard DSO counts both piles. Best possible DSO counts only the current pile.

By removing overdue balances from the math, best possible DSO answers a focused question: if customers paid right on the due date and never a day later, what would our DSO be? That number is roughly equal to your average payment terms, and it is the best your current term structure allows. You cannot beat it without changing terms or collecting early.

Best possible DSO formula

The formula mirrors standard DSO but swaps total receivables for current receivables:

Best Possible DSO = (Current Receivables / Total Credit Sales) x Number of Days

Current receivables means the balance that has not yet passed its due date. Total credit sales and the day count match the period you are measuring, just as they do for days sales outstanding.

Worked example

Take a company with 600,000 in total accounts receivable at month end, of which 420,000 is current and 180,000 is overdue. It booked 750,000 in credit sales that month.

First, standard DSO using the full balance:

Standard DSO = (600,000 / 750,000) x 30 = 24 days

Now best possible DSO using only current receivables:

Best Possible DSO = (420,000 / 750,000) x 30 = 16.8 days

The gap is 24 minus 16.8, or about 7.2 days. That 7.2 days is the collectible opportunity. If the company cleared its overdue balance and kept it clear, DSO would drop from 24 to about 17 with no change to terms and no new sales.

That gap also translates straight into cash. At 750,000 of monthly credit sales, one day of DSO is worth roughly 25,000 (750,000 divided by 30). So the 7.2-day gap represents about 180,000 in cash sitting in overdue invoices, money the business has already earned but not yet collected. Framing the gap in dollars rather than days is often what gets a collections improvement funded.

Best possible DSO vs standard DSO

The two metrics are most useful side by side. Standard DSO is your actual performance. Best possible DSO is your ceiling given current terms. The difference between them, often called the DSO gap, is the part of your collection time that is genuinely fixable.

A small gap means your collections are tight and most of your DSO comes from the terms you offer, not from slow follow-up. A wide gap means real cash is stuck in overdue invoices that better collections could pull forward. Two companies can report the same 24-day DSO, but the one with a 2-day gap is running a clean ledger while the one with a 9-day gap has a recovery opportunity hiding in plain sight.

The gap is also a cleaner target than DSO itself. You cannot fairly ask a team to beat the floor set by your payment terms, but you can ask them to close the gap to it. It also makes comparison across business units or regions fair. A division selling on net 60 will always report a higher DSO than one selling on net 15, but if both run a 3-day gap, both are collecting equally well relative to the terms they offer. Benchmarking on the gap rather than raw DSO stops you from punishing a team for terms it did not set.

How to close the DSO gap

Closing the gap means keeping current invoices from ever becoming overdue, and clearing the overdue pile that already exists. The moves that matter:

• Work invoices the moment they age past due, before a 5-day slip becomes a 30-day one.
• Remind customers before the due date so current invoices stay current.
• Resolve disputes quickly, since a disputed invoice sits in the overdue pile until it clears.
• Prioritize the largest current balances at risk of slipping, since those move the gap most.

The pattern is prevention plus prompt cleanup. The closer you keep every account to its due date, the closer your actual DSO drifts toward its best possible floor. The cleanest signal of progress is simply watching the gap shrink month over month.

How Rex closes the gap to best possible DSO

The gap closes when current invoices never slip and overdue ones get worked at once. That is continuous, account-by-account work, and it is exactly what Rex does. Rex is an autonomous accounts receivable agent that watches every invoice as it approaches its due date, reminds the customer in time to keep it current, and moves on the same day an account ages past terms. Because it runs across the entire ledger without waiting for a free afternoon, current invoices stop drifting into the overdue pile in the first place.

For the overdue balances that already exist, Rex pursues them in priority order and escalates the genuine edge cases, a disputed charge or a customer asking for a payment plan, to a person with the context ready. The result is an actual DSO that tracks much closer to its best possible floor.

See how Rex keeps current receivables current and shrinks the gap to your best possible DSO.