Key takeaways
- Net profit per unit is the cash one sale leaves after COGS, referral fee, FBA fulfilment fee, inbound freight, storage, PPC, a returns allowance, and allocated overhead.
- UK sellers must extract VAT before calculating, because Amazon's referral fee is charged on the ex-VAT price and gross revenue overstates profit by over £4 per unit at 20% VAT.
- PPC cost per unit is total ad spend divided by total units sold, including organic and halo sales, not just ad-attributed units.
- Breakeven ACOS equals pre-PPC net profit per unit divided by selling price; scale campaigns below that line and fix or cut anything above it.
- Absolute pounds per unit beats percentage margin for reorder decisions because you restock inventory in currency, not margins.
Net profit per unit is the cash one sale leaves after COGS, referral fee, FBA fulfilment fee, PPC, a returns allowance, and your share of fixed overhead. Build it once per SKU and you can set a breakeven ACOS, price correctly, and know before you reorder whether that product actually pays you.
What is net profit per unit and how does it differ from net profit margin?
Net profit per unit is the cash a single sale leaves behind after Amazon's referral fee, FBA fulfilment fee, COGS, and your share of PPC, storage, and refunds. Net profit margin is the same maths across your whole business, expressed as a percentage of revenue.
The difference matters because margin hides the SKU that quietly eats your reorder cash. A blended 15% margin can contain one product at £4.50 per unit and another at -£1.20, and only the per-unit view shows which one to fix or cut. That is why a Reddit seller put it plainly: ACOS tells you what the ad did, not whether the SKU pays for itself (r/FulfillmentByAmazon thread). Amazon's own fee schedule (Seller Central) is where the per-unit inputs start.
What is the net profit per unit formula?
Net profit per unit is everything you take out of one sale, minus everything that sale costs you, divided by units sold:
Net profit per unit = (Net selling price − COGS − referral fee − FBA fulfilment fee − inbound freight per unit − storage allowance − PPC cost per unit − returns allowance − allocated overhead) ÷ units sold
The net selling price is what the customer actually paid after VAT (UK) and any discount or promotion, not your list price. Each deduction is a per-unit figure: if your inbound shipment covered 500 units, divide the freight bill by 500. Returns get an allowance, not the full refund, because only a percentage of orders come back.
The formula template you can copy into a spreadsheet
Set up one row per deduction and one column per SKU. Rows: net selling price, COGS, referral fee (15% for most categories), FBA fulfilment fee, inbound freight, storage allowance, PPC per unit, returns allowance, overhead. Net profit per unit is a single SUM at the bottom. If you want the arithmetic pre-built, our FBA profit calculator follows the same structure.
How do you allocate fixed costs to individual units?
Fixed costs do not show up on a per-unit receipt, so you have to divide them in yourself. Three costs need this treatment: storage, returns, and your overhead. Get the allocation window wrong on any of them and your net profit per unit will lie to you in both directions.
Storage fees
Amazon bills storage monthly, whether or not a unit sells. Divide the month's storage bill by the units sold that month. If storage cost £180 and you sold 600 units, that is £0.30 per unit. Aged or oversized inventory will skew this badly, which is the point: the skew is real and belongs in the unit economics. Amazon's own fee schedule, including the monthly and long-term surcharge structure, is documented in Seller Central's FBA storage fees help page.
Returns allowance
You cannot know which unit comes back, so spread the cost across all units. Take your refund rate, multiply it by the full unit economics it destroys: refunded revenue, the outbound FBA fee, and the COGS you rarely recover. A 4% refund rate on a £20 unit with £8 in fees and COGS costs you roughly £1.12 per unit sold. That number belongs in the formula, not in a footnote.
Overhead: the monthly-units method
Your other fixed costs, software subscriptions, accountant fees, and the rest, get the simplest treatment: total monthly overhead divided by monthly units sold. The honest answer on window choice is that no single window is correct, only defensible. A month is too volatile for a seller with 200 units and one storage surprise; a quarter smooths that noise but hides a genuine decline if you only check quarterly. Use a rolling 90-day window for storage and overhead, recalculate monthly, and re-run it whenever you add a SKU or change your reorder cadence. The window matters less than picking one and never changing it mid-comparison, because a per-unit figure that moves because the denominator moved will wreck every pricing and PPC decision downstream. If you want that recalculation to arrive as a single Monday-morning action instead of a spreadsheet session, SellerMatrix's affiliate programme reflects the same weekly-review approach the product itself runs on.
Worked example: net profit per unit for a US FBA sale
Take a $29.99 product and run every line through the formula. Assume COGS of $6.50, a $2.00 inbound cost per unit, and a $1.20 monthly overhead allocation (software, accountant, storage buffer spread across units sold).
| Line | Amount |
|---|---|
| Sale price | $29.99 |
| Referral fee (15%) | −$4.50 |
| FBA fulfilment fee | −$4.75 |
| COGS | −$6.50 |
| Inbound per unit | −$2.00 |
| PPC per unit | −$2.40 |
| Returns allowance (3% × $10.25 cost stack) | −$0.31 |
| Overhead allocation | −$1.20 |
| Net profit per unit | $8.33 |
Two notes. First, the returns line is an allowance, not a guess: 3% of the costs you never recover per returned unit. Second, PPC per unit here is ad spend divided by total units sold, not ad spend divided by ad-attributed units. If your ACOS suggests $2.40 is too high, check your breakeven point with our ACOS calculator before touching bids. At $8.33, this SKU funds its own reorder and still leaves margin.
Worked example: UK sale with VAT
Same product, UK listing: £24.99 including VAT at 20%. Extract VAT first, because Amazon's referral fee is calculated on the ex-VAT price, and every downstream number changes if you skip this step. Ex-VAT price: £24.99 ÷ 1.20 = £20.83.
Now the cost stack, all per unit:
- Referral fee (15% of £20.83): £3.12
- FBA fulfilment fee: £3.00 (illustrative)
- COGS: £6.00
- Inbound shipping: £0.50
- Storage allocation: £0.15
- Returns allowance (1.5% of price): £0.40
- PPC cost: £1.50
Net profit per unit = £20.83 − 3.12 − 3.00 − 6.00 − 0.50 − 0.15 − 0.40 − 1.50 = £6.16.
Two UK-specific traps: referral and FBA fees come out of the VAT-exclusive figure, and VAT itself is never your money, so it must not sit in your reorder cash. If you priced the US way and treated £24.99 as revenue, you would overstate profit by over £4 per unit.
How do you calculate net profit per unit when PPC is involved?
From ad spend to ad cost per unit
Ad cost per unit is total ad spend divided by total units sold, where total units include the halo sales that ads drive. If you spent $300 and sold 60 ad-attributed units plus 40 organic units you believe the ads influenced, your ad cost per unit is $300 ÷ 100 = $3.00. Dividing by total units rather than attributed units matters because the halo is real but invisible in the Ads console.
Breakeven ACOS from net profit per unit
ACOS is ad spend divided by ad sales, per Amazon's advertising documentation. Breakeven ACOS is your pre-PPC net profit per unit divided by your selling price. A unit selling at $25 with $8 of profit before ads has a breakeven ACOS of 32%. Below that, ads add profit; above it, they eat reorder cash.
What is a good net profit per unit for an e-commerce product?
There is no universal number, because a "good" figure depends on your price point and fee load. A £15 product might net £2.50 per unit (17%), while a £60 product might net £9 (15%) and still leave you far more reorder cash per sale.
That is why absolute pounds per unit beats percentage: you reorder inventory in currency, not margins. £1.20 per unit on 400 units a month gives you £480 of reorder cash; 22% on a slow SKU gives you almost nothing.
Set a floor per SKU instead of chasing a benchmark: your COGS plus inbound shipping per unit, plus a buffer for storage fees and refunds. If a SKU's net profit per unit drops below that floor, it cannot pay for its own restocking, whatever its margin says.
How can you use net profit per unit to make pricing and product-line decisions?
Take the US example from earlier: £4.10 net profit per unit. A £1 price rise on an inelastic SKU flows straight to £5.10 per unit, so 100 units a week adds roughly £400 of reorder cash a month. If the price rise costs you 10% of units, you still come out ahead.
The PPC cut decision uses breakeven ACOS. If your margin per unit before ads is £6.50, breakeven ACOS is about 63%, so a campaign running at 40% ACOS has headroom, while one at 70% is burning reorder cash on every sale.
The delist decision is the blunt one: a SKU at £0.40 net per unit ties up the same reorder cash and shelf attention as one at £4.10. Cut it and redeploy the stock. When checking VAT-inclusive UK prices before a rise, extract the VAT first using the GOV.UK guidance (VAT rates, charges and rules), or your per-unit maths runs on the wrong base.
What are common mistakes when calculating profit per unit?
Five errors account for most wrong numbers.
Using gross margin instead of net: subtracting only COGS from price and ignoring FBA fees, referral fees, and storage means a SKU that looks healthy is quietly losing money per unit.
Skipping a returns allowance: if 4% of units come back and refunds cost you the referral fee plus return shipping, that belongs in every unit's math, not a mental note.
Allocating overhead to nothing: fixed costs like software subscriptions only work in the formula if every unit sold carries its share.
Mixing VAT into revenue: UK sellers must subtract VAT from the sale price before calculating anything, or every figure is inflated by 20%.
Trusting ACOS alone: ACOS says what ads cost, not whether the unit survives fees and returns. Check breakeven ACOS against net profit per unit before scaling spend.
FAQ
Does net profit per unit include PPC spend?
Yes. PPC belongs in the formula because ad spend is a real per-unit cost. Divide total ad spend by total units sold, including organic and halo sales, not just ad-attributed units. A $300 campaign across 100 total units adds $3.00 to every unit's cost stack. Leaving PPC out inflates your figure and hides whether the SKU survives its own advertising.
How do I work out profit per unit after refunds and returns?
Use a returns allowance rather than waiting for actual refunds. Multiply your refund rate by the full cost a return destroys: the refunded revenue, the outbound FBA fee, and the COGS you rarely recover. A 4% refund rate on a £20 unit with £8 in fees and COGS costs about £1.12 per unit sold. Add that allowance as a line in the formula.
Should I calculate net profit per unit with VAT included or excluded?
Excluded, always. VAT is never your money, so it must not sit in your reorder cash. Extract it first, because Amazon's referral fee is calculated on the ex-VAT price and every downstream number changes if you skip that step. A £24.99 UK price is £20.83 of revenue at 20% VAT. Treating the gross figure as revenue overstates profit by over £4 per unit.
What net profit per unit do I need before scaling ads?
Work out breakeven ACOS instead of chasing a fixed number: divide your pre-PPC net profit per unit by your selling price. A $25 unit with $8 of profit before ads breaks even at 32% ACOS. Scale campaigns below that line and cut or fix anything above it. Also set a per-SKU floor, typically COGS plus inbound plus a buffer, so ads never eat your reorder cash.