How do I calculate days sales outstanding?

Divide ending accounts receivable by total credit sales for the period, then multiply by the number of days in that period. Use credit sales only, not total revenue, and be consistent about the period length (30, 90, or 365 days) so DSO trends over time are actually comparable to each other.

By Zuny Fester, Head of Operations and Marketing

Reviewed by Zuny Fester

Published September 10, 2026Last reviewed September 10, 2026Editorial policy

Part of the accounts receivable and collections guide.

Formula	(Accounts receivable / Credit sales) × Number of days
Use	Credit sales only, not total revenue including cash sales
Common period lengths	30 (monthly), 90 (quarterly), or 365 (annual) days
Consistency requirement	Use the same period length each time to compare trends fairly

Step by step

Take the ending accounts receivable balance for the period being measured. Divide it by total credit sales for that same period — excluding cash sales, since they don't generate a receivable. Multiply the result by the number of days in the period (30 for a month, 90 for a quarter, 365 for a year) to get DSO expressed in days.

Common mistakes that distort the number

Using total revenue instead of credit sales inflates or deflates DSO depending on how much of revenue is cash-based. Switching period lengths between calculations (comparing a 30-day DSO to a 90-day one without adjusting) makes trend comparisons meaningless. Using an average AR balance instead of the ending balance is also common and defensible, but should be applied consistently, not switched between periods.

Prefer to plug in your own numbers? Use the free DSO calculator — it runs this exact formula.

Next step

Map the finance workflow with the most exposure and prove the automation path.

Bring the invoice, contract, payment reconciliation, or customer finance workflow you have to defend at audit. Loopfour can map the trigger, controls, integrations, and approval loop.

Book a workflow review

Worked example

The calculation with real numbers

Ending AR: $450,000. Credit sales for the quarter: $2,700,000. Period length: 90 days. DSO = ($450,000 / $2,700,000) × 90 = 15 days. If the same company had instead used total revenue of $3,000,000 (including $300,000 of cash sales), DSO would incorrectly calculate as ($450,000 / $3,000,000) × 90 = 13.5 days — understating the true collection period by excluding the fact that only credit sales generate the receivable being measured.

Frequently Asked Questions

Either is defensible — average AR smooths out timing spikes, ending AR is simpler — but pick one method and use it consistently so period-to-period comparisons stay meaningful.

The formula is the same, but seasonal businesses should be cautious comparing DSO across periods with very different sales volumes, since the denominator itself swings seasonally.

Yes — the same formula applied to one customer's AR balance and credit sales gives a useful, more targeted view for account-level credit decisions.

Sources

Topic

AR & Collections

Accounts receivable is the money customers owe a business for goods or services already delivered on credit — a current asset on the balance sheet until it's collected. AR and collections, as a practi…

Definition

What is days sales outstanding?

Days sales outstanding (DSO) is the average number of days it takes a company to collect payment after a sale, calculated as accounts receivable divided by credit sales, multiplied by the number of days in the period. A lower DSO means faster cash conversion; a rising DSO signals collections are slowing relative to sales.

How-to

How do I reduce days sales outstanding?

Send accurate invoices promptly, offer multiple payment methods, automate payment reminders, follow up systematically on overdue accounts, and review outstanding receivables regularly. Most DSO reduction comes from removing friction and delay in the invoice-to-cash cycle, not from pressuring customers harder.