Days Inventory On Hand (DOH) tells you how many days a company typically sits on its inventory before selling it.

It's one of three metrics -- alongside Days Sales Outstanding and Days Payable Outstanding -- that together determine the cash conversion cycle: how long it takes a business to turn a dollar of operating spend into a dollar of cash in the bank.

That's why DOH matters. The lower your inventory days, the less cash gets tied up on the shelf, and the less working capital you need to fund the business.

This post covers what DOH measures, how to calculate it (including in Excel), what a "good" number looks like by industry, and how FP&A teams and PE firms use it in practice.

What Days Inventory On Hand Actually Measures

Days Inventory On Hand (or DOH, sometimes called "inventory days") tells you how many days of stock a company typically keeps on the shelf.

Or said another way: how many days it would take the business to sell out of inventory if it stopped buying tomorrow.

If your DOH is 60 days, it takes the company roughly two months to turn inventory into revenue. If it's 180, the company has half a year of stock sitting around. Neither is automatically good or bad. Context is everything (more on that below).

DOH is one of three working capital timing metrics finance teams track together:

• DSO (Days Sales Outstanding): how long it takes to get paid by customers
• DOH (Days Inventory On Hand): how long inventory sits before being sold
• DPO (Days Payable Outstanding): how long the company takes to pay suppliers

Each one measures a different stage of the working capital cycle, and together they tell you how efficiently the business is converting operating activity into cash.

The Days Inventory On Hand Formula

The standard DOH formula is:

DOH = (Inventory ÷ COGS) × Number of Days in Period

So if a company has $2M in inventory and $12M in COGS over 12 months, the annual DOH is:

(2,000,000 ÷ 12,000,000) × 365 = 61 days

Two things to know about this formula.

First, the period matters. For an annual calculation, use 365 days. For a quarterly calculation, use 90. For a monthly calculation, use 30. If you're building a rolling monthly tracker, you can also use an LTM (last twelve months) denominator with 365 days in the numerator -- that gives you a smoother, less volatile reading.

Second, which inventory balance do you use? You have three options:

• Ending inventory (snapshot as of the period end)
• Beginning inventory (balance at the start of the period)
• Average inventory ((beginning + ending) ÷ 2)

For a point-in-time reading, ending inventory is fine. For a metric you're going to use in forecasting and trend analysis, I'd use average -- it smooths out the timing quirks of when purchases land.

How DOH Fits Into the Cash Conversion Cycle

DOH doesn't stand alone. It's one-third of the cash conversion cycle (CCC), which tells you how long it takes the company to turn a dollar of operating spend into a dollar of cash in the bank.

CCC = DSO + DOH − DPO

In plain English: how long does cash get tied up in the business?

• DSO tells you how long on average it takes you to collect cash from customers
• DOH tells you how long your cash sits on warehouse shelves
• DPO tells you how long you get to sit on your vendors' cash (fun fact: this is someone else's DSO).

The lower the CCC, the less working capital you need to fund operations. Some businesses (Amazon being the classic example) actually run a negative cash conversion cycle -- they collect from customers before they have to pay suppliers, which means growth actually generates cash instead of consuming it.

For most businesses though, CCC is positive, and DOH is usually the biggest lever. DSO and DPO tend to be governed by customer and vendor terms that are hard to renegotiate. Inventory is something the operations team can actually control.

Calculating DOH in Excel

For FP&A teams, DOH typically lives in a working capital schedule inside a three-statement model. Here's the basic setup.

Let's say you have monthly historical data: revenue, COGS, and balance sheet line items including inventory.

1. Below your historical financial statements, create a working capital statistics section.
2. For each month of history, compute DOH using:
   • =(Inventory_Cell / SUM(Trailing_3_Month_COGS)) * 90.
   • I prefer 90 days because it gets rid of lumpy monthly noise, but isn't so smooth (like 180 days) that you lose the up and down movements of cash. It's a nice middle ground.
3. Format the output as a number with one decimal place, with a label like "DOH (90-day)."
4. Drag the formula across your historical period and trend the result.

Once you have the historical, the real benefit is leveraging that information into a forecast.

5. Calculate the average DOH over the last 6 to 12 months (or just link to your most recent calculation).
6. In your forecast period, use that assumption as the driver for future inventory:
   • Inventory = (Forecast_COGS / 90) * DOH_Assumption.
7. Now your inventory balance flexes with COGS automatically. If COGS grows 10%, inventory grows 10%. If you assume operational improvement, you lower the DOH assumption and inventory compresses.

This is how you build a working capital forecast that's dynamic instead of hardcoded. And it's how you turn DOH from a backward-looking metric into a forward-looking one.

(If you want a full walkthrough of this approach inside a three-statement model -- including how the working capital schedule feeds the balance sheet and cash flow statement -- that's what the program covers.)

What's a "Good" Days Inventory On Hand? It Depends.

There is no universal "good" DOH number.

What matters is the context. A few rough reference points by industry:

• Grocery and perishables: Low DOH is essential. Often 15-30 days. Anything above that risks spoilage.
• Apparel and seasonal retail: Typically 60-120 days, driven by season buys and markdown cycles.
• Industrial and manufacturing: Often 60-120 days, though it varies wildly by product and supply chain.
• Distribution and wholesale: Can run 30-90 days depending on product mix and turnover.
• SaaS and services: Not applicable -- no inventory.  You're selling contracts, but nothing "physical."

Even within the same industry, two companies can have very different "correct" DOH numbers depending on supplier lead times, demand volatility, product mix, and inventory strategy. Use the benchmark as a reference point, then dig into the specifics.

The more important question is what the trend is telling you.

Rising DOH usually means one of three things: sales are slowing (and inventory isn't moving), the company is overbuying (bad purchasing discipline), or there's obsolete stock building up (future write-down risk). None of these are good news.

Falling DOH usually means either genuine operational improvement or demand has outpaced the supply chain's ability to restock. The second case can mean stockouts and lost sales, so "lower is always better" is not the right read.

Ultimately, just make sure you're looking at the trend.

Why FP&A Teams Should Track DOH Every Month

If you're in FP&A and you're only looking at DOH quarterly, you're missing its most valuable use: as an early warning.

Rising DOH is a leading indicator of cash flow pressure. Inventory on the shelf is cash you've already spent. As DOH rises, your cash balance falls (or your revolver draws increase), even if the income statement still looks healthy.

Three specific ways FP&A teams should use DOH:

1. In the monthly reporting package. Alongside the variance analysis for COGS and inventory, report DOH month-over-month and versus prior year. If DOH is up, that's a line item worth calling out to leadership.

2. In the working capital forecast. DOH directly drives your projected inventory balance in a three-statement model. If you get the DOH assumption wrong, your balance sheet and your cash flow forecast will both be wrong.

3. In variance analysis. When cash comes in lower than forecast, DOH is usually one of the first places to look. Higher DOH than you assumed means more inventory than planned means less cash than planned.

How Private Equity Firms Use DOH

PE firms use DOH the same way FP&A teams do -- as a monthly tracking metric built directly into the operating model. I build it into every LBO model I put together. On top of that, DOH gets used during diligence as a peer benchmarking tool.

When a PE firm is looking at a target company, DOH is one of the first operational metrics they'll benchmark against peers. A target with materially higher DOH than its industry comps has one of two things: an operational improvement opportunity (good for the PE thesis) or a structural reason for the gap that needs to be understood (could be fine, could be a red flag).

PE operating partners will specifically look at:

• DOH trend over the last 3-5 years: Is this a company that's getting better or worse at inventory management?
• Peer benchmarking: Where does DOH sit versus public comps and other portfolio companies?
• Composition of inventory: Is the DOH number being driven by raw materials, WIP, or finished goods? Each tells a different story.
• Obsolescence reserves: High DOH with low reserves can mean a hidden write-down.

If you're presenting a business to PE investors or preparing for a sale process, you need to know your DOH cold and have a clear story about the trend.

Common Mistakes When Calculating DOH

A few traps I see regularly:

1. Mixing period conventions. If your inventory is a snapshot at quarter-end, don't divide it by full-year COGS. Keep the period consistent.
2. Ignoring seasonality. A Q4 DOH reading for a holiday retailer will look very different from a Q2 reading. Compare like to like (year-over-year same-quarter, not sequential).
3. Treating DOH as pass/fail. A number going up without operational context is the actual problem. Always tie movement to what's happening in the business.
4. Using it in isolation. DOH is most useful alongside DSO, DPO, and the cash conversion cycle. Look at the full working capital picture.

Key Takeaways

• DOH measures how many days of inventory a company typically holds, calculated as (Inventory ÷ COGS) × Days in Period.
• A "good" DOH depends on industry, product mix, and trend. Use benchmarks as a reference point and dig into the specifics.
• Rising DOH is a leading indicator of cash flow pressure. FP&A teams should track it monthly.
• PE firms use DOH as a monthly tracking metric in their operating models and as a benchmarking tool in diligence.
• DOH is most useful when viewed alongside DSO and DPO as part of the cash conversion cycle.

Want to Build This Into a Full Model?

This post covered the concept. If you want to actually build a working capital schedule that uses DOH as a forecast driver (inside a proper three-statement model that balances and flows through to cash), that's exactly what the Mastery Program teaches.

The program walks through the full working capital build -- DSO, DOH, DPO, the cash conversion cycle, and how to link it all into the balance sheet and statement of cash flows. Fundamentals first, so that when you use AI to accelerate your modeling, you actually know what the model is doing.