DSO, DPO and inventory days
Three ratios turn a balance sheet into a story about time. Calculated properly, they show how long a client waits to be paid, how long it takes to pay its vendors, and how long its inventory sits before it sells.
On Business Training · September 1, 2026 · 5 min read
A balance sheet shows what a business owned and owed on one day. On its own it says little about how fast money moves through the business. Three ratios fix that: days sales outstanding (DSO), days payable outstanding (DPO) and inventory days. Each converts a balance into a number of days. A lender can compare days with payment terms, with last year, and with the A/R aging in front of it.
The three formulas
- DSO = accounts receivable ÷ net sales × 365. How long, on average, customers take to pay.
- Inventory days = inventory ÷ cost of goods sold × 365. How long goods sit before they are sold.
- DPO = accounts payable ÷ purchases × 365. How long the business takes to pay its vendors. Purchases are rarely broken out in the financial statements, so cost of goods sold is the usual stand-in.
Use the year’s net sales and cost of goods sold, and the balances at year end. For a period other than twelve months, use the number of days in the period instead of 365. Use trade receivables and payables only: an officer loan or a tax refund receivable doesn’t belong in DSO.
A worked example
Fenwick Packaging Inc.’s year-end financial statements show:
| $ | |
|---|---|
| Net sales | 2,400,000 |
| Cost of goods sold | 1,680,000 |
| Accounts receivable | 400,000 |
| Inventory | 210,000 |
| Accounts payable | 252,000 |
Then:
- DSO: 400,000 ÷ 2,400,000 × 365 = 60.8 days
- Inventory days: 210,000 ÷ 1,680,000 × 365 = 45.6 days
- DPO: 252,000 ÷ 1,680,000 × 365 = 54.8 days
Reading the numbers
Against terms. If Fenwick sells on net 30 terms, DSO of 61 means customers are paying, on average, a month late. If its terms are net 60, 61 is about right. The ratio means nothing until you know the terms.
Against last year. A rise from 48 to 61 days in a year is worth a question even if both are within terms. It may be one large, slow customer. It may be disputes building up, or a shift in the kind of customer the client sells to.
Against the receivables you fund. You have something an ordinary reader of financial statements doesn’t: the client’s A/R aging, every month. DSO from the financial statements is a single year-end figure. The aging tells you whether the year end was typical. If the statements show 45 days and the receivables you fund have never turned faster than 60, one of them needs explaining.
Inventory days rising while sales are flat often means inventory that won’t sell. It may be carried at cost on the balance sheet but be worth far less. DPO rising can mean the business is using its vendors as a bank. That is free financing until a vendor puts the account on credit hold.
Put them together
Add DSO to inventory days and subtract DPO, and you have the cash conversion cycle: how many days the business must fund between paying for goods and collecting for them.
For Fenwick: 60.8 + 45.6 − 54.8 = 51.6 days.
Every day in that cycle has to be financed by someone: the owners, a bank line, or a facility like yours. If the cycle stretches as the business grows, the funding need grows faster than sales. That is how profitable companies run out of cash, and why DSO matters so much to a factor.
The aging tells you more
DSO compresses the whole ledger into one number, and averages hide things. A client can report a steady DSO while one large customer slides into 90 days past due and many small ones pay faster. So read DSO next to the A/R aging. If the share of receivables over 60 days past invoice is growing, the average may not show it for months. The aging also shows cross-aging risk, which DSO never will.
Cautions
- One day is not a year. Year-end balances can be unusual. A seasonal business may close its fiscal year at its quietest point. Window dressing can flatter DSO, such as a big collection push in the last week of the year.
- Compare like with like. Construction, distribution and retail all have different normal patterns. Compare a client with its own history first and its industry second.
- Know what you’re reading. Audited, reviewed and compiled financial statements give different levels of assurance. In-house interim statements give none. Check the CPA’s report before relying on the balances.
- Mind the averages. Some lenders calculate DSO using average receivables for the year rather than the year-end balance. Either is fine, as long as you use the same method every time you compare.
Calculated carefully, three ratios give a lender an early sign of slow-paying customers, unsold inventory and stretched vendors. Each one is worth a question at the next review.