The inventory payback formula
Net gain from funded inventory equals the gross profit on the goods you sell minus the funding cost and any added carrying costs such as storage, insurance and shrink. Gross profit is revenue from those goods minus what they cost you. If net gain is clearly positive in a realistic scenario, the funding can pay back.
Gross profit = revenue from the goods − cost of the goods
Net gain = gross profit − funding cost − added carrying costs
Example: $40,000 of goods priced for a 35 percent gross margin have a full-price value of about $61,538. If everything sells at full price, gross profit is about $21,538. Subtracting a $6,000 funding cost leaves about $15,538. These are illustrative figures, not a forecast or a quote.
Margin versus markup: get this right first
Margin is gross profit as a share of the selling price; markup is gross profit as a share of cost. Mixing them up overstates profit. A 50 percent markup is only a 33 percent margin. Use margin in the payback formula, because funding cost has to come out of the profit on each sale.
Margin = (price − cost) ÷ price
Markup = (price − cost) ÷ cost
Example: an item that costs $20 and sells for $30 has a $10 gross profit. That is a 50 percent markup but a 33 percent margin. If an owner mistakes that 50 percent markup for a 50 percent margin, they will expect $30,000 of gross profit on $60,000 of sales when the real figure is about $20,000, and a funding cost that looked easy to cover can swallow much of the real profit. Illustrative only.
| Scenario | Revenue | Gross profit | Net gain after funding and carrying costs |
|---|---|---|---|
| All sells at full price | $61,538 | $21,538 | $15,538 |
| 80% full price, rest 30% off | $57,846 | $17,846 | $11,846 |
| 60% full price, rest 50% off, +$800 storage | $49,231 | $9,231 | $2,431 |
Turn speed: how long the money is tied up
Payments on funding usually start right away, but revenue from inventory arrives as goods sell. The slower the goods turn, the longer you carry payments before the money comes back, and the more carrying costs build. Estimate months to sell from your own sales history for the same or similar items.
Months to sell = units bought ÷ average units sold per month
Example: if a store sells 500 units of an item a month and funds a purchase of 1,500 units, the stock lasts about three months. A six-month funding term means payments continue for three months after the stock is gone, which works only if other sales carry them. A two-month term means the payments finish before the goods have sold, pulling cash from elsewhere in the meantime. Illustrative only.
Match the term to the turn
A good match lets sales from the funded goods cover the payments as they come due. A term much shorter than the turn forces you to pay from other cash before the goods sell. A term much longer than the turn usually costs more in total and keeps a payment running after the inventory is gone.
For repeat purchases that turn on a steady cycle, a line of credit drawn per order and repaid as goods sell can cost less than a lump sum. For a single seasonal buy, compare working capital options, converting each to a monthly figure first.
Markdowns and slow sell-through
Most inventory does not all sell at full price. Leftovers get discounted, and each markdown cuts gross profit while the funding cost stays the same. Run at least three scenarios: everything sells at full price, most sells with some markdowns, and a slow case with deeper discounts and extra carrying cost.
Example: if 80 percent of the $40,000 buy sells at full price and the rest at 30 percent off, gross profit falls to about $17,846 and net gain to about $11,846. If only 60 percent sells at full price, the rest goes at half price and storage adds $800, net gain drops to about $2,431. The table sets the three side by side. Illustrative only.
What margin makes inventory funding too expensive?
Calculate break-even revenue: the cost of the goods plus the funding cost plus carrying costs. Then ask what share of full-price value you must collect to reach it. If your realistic sell-through, after markdowns, falls below that share, the funding costs more than the inventory earns.
Break-even revenue = cost of goods + funding cost + carrying costs
Example: $40,000 + $6,000 = $46,000. Against a full-price value of about $61,538, you need to collect about 75 percent of full price across the whole buy, meaning your average discount cannot exceed about 25 percent. Illustrative. See how this plays out for retail stores and distributors.
Frequently asked questions
How do I calculate gross profit on inventory?
Subtract the cost of the goods from the revenue you expect when they sell. Use realistic selling prices, including likely discounts, not list prices. If you track margin as a percentage of price, gross profit equals revenue times margin. Make sure you are using margin, not markup, or the result will be too high.
What if the inventory sells slower than planned?
Payments continue on schedule while sales lag, so you cover them from other cash, carrying costs grow, and markdowns become more likely. Before funding, run a slow scenario with a longer sell-through period, deeper discounts and added storage, and confirm the net gain stays positive and the payments stay affordable.
Should the funding term match the inventory turn?
Ideally, yes. A term close to the time it takes the goods to sell lets their sales cover the payments. A much shorter term means paying from other cash before the goods sell; a much longer term usually raises total cost and keeps a payment running after the inventory is gone.
How do discounts and markdowns change the math?
Each markdown lowers revenue while the cost of goods and the funding cost stay fixed, so it comes straight out of net gain. In an illustrative case, moving from all full-price sales to a slow scenario with half-price leftovers cut net gain by more than 80 percent. Always test a markdown scenario.
What margin makes inventory funding too expensive?
It is too expensive when the revenue you realistically collect cannot cover the cost of the goods plus the funding and carrying costs. Calculate break-even revenue, divide it by full-price value, and compare that share with your usual sell-through after markdowns. If you rarely reach it, do not fund the buy.
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Updated September 14, 2026 · Roifunder Funding Team