Amazon FBA Profit Calculator Spreadsheet: Real Margin Per SKU

You know your revenue. Seller Central puts it on the first screen in a font you cannot miss. What it does not put anywhere is the number you actually need: what one unit of one SKU leaves in your pocket after Amazon has taken its cut three separate times, after the container freight, after the ads that got the sale, and after the two units in every forty that come back.

Most sellers work this out once — in a fee calculator, before they place the first order — and never look again. Then the fee schedule changes, the packaging grows a quarter inch and jumps a size tier, PPC creeps up, and eighteen months later the product that was going to make $10 a unit is making $4 and nobody noticed, because the revenue line never stopped going up.

This guide builds the spreadsheet that notices. One row per SKU, a settings tab holding your fee assumptions, and a monthly roll-up that walks you from the per-unit number down to the money in the bank.

Every figure below runs on one worked example so you can follow the arithmetic. The fee amounts are assumptions I have chosen to be plausible, not quoted rates. Amazon’s referral percentages vary by category, fulfilment fees depend on your size and weight tier, and storage rates change through the year. Read your own from Seller Central and replace mine. The structure is what transfers.

The example SKU

BAM-CUT-01 — a bamboo cutting board. Assumptions for the whole guide:

Hold on to those. They come back in every section.

Layer 1: the settings tab, because assumptions belong in one place

Before a single SKU row exists, build a settings tab holding your defaults: referral percentage, fulfilment fee, storage per unit, inbound shipping per unit, the monthly Professional plan fee, your target margin, your target ROI, and your estimated return rate.

Then every SKU row reads from those defaults unless you override it on the row.

This sounds like housekeeping. It is the single most valuable structural decision in the whole spreadsheet, for one reason: Amazon changes its fee schedule, and when it does you want to change one cell, not forty. A seller with hardcoded fees discovers a fee increase when the payout drops. A seller with a settings tab types a new number into one cell and watches which SKUs turn red.

Set the two goal lines here too — a target net margin (20% is a common floor) and a target ROI (many FBA sellers will not reorder below 50%). Those two numbers turn the catalogue tab from a list into a decision.

Layer 2: the per-unit calculation

Nine columns per SKU. Yellow ones you type, the rest calculate.

Two details in that table do more work than they look like they do.

Referral has to be a formula, never a typed dollar amount. It is a percentage of the sale price, so it moves every single time you reprice. A seller who drops a product from $24.99 to $21.99 to win the Buy Box and leaves a hardcoded $3.75 referral in the sheet has understated their fees and overstated their margin at exactly the moment they most needed the truth.

The FBA fulfilment fee is per row, not global. It is set by size and weight tier, so a fulfilment fee that is right for a cutting board is nonsense for a dog bed. Leaving the default $5.45 on an oversize product is the most common way an FBA spreadsheet lies to its owner — and it lies in the flattering direction. Look up the tier for each SKU once and put the real number on the row.

Layer 3: margin and ROI are different questions

The cutting board posts a 41.4% margin and a 211% ROI. Those two numbers feel like they are saying the same thing. They are not.

Margin is a resilience number. It tells you how much room the product has before it stops working. A 41% margin can absorb a fee increase, a competitor’s price war and a bad ad month, and still be worth selling. A 12% margin cannot absorb any of them.

ROI is a capital-efficiency number. It tells you how hard each dollar you spend on inventory is working. When you have $20,000 and four products asking for it, ROI is the tiebreaker, because the highest-margin product is not always the one that turns your cash the most times a year.

Set both goal lines in settings and add a status column that reads green if margin ≥ target AND ROI ≥ target, amber if one, red if neither. Sort the catalogue by that column and you have a reorder list instead of a spreadsheet.

The version of this you run before you buy anything is the break-even price — the lowest number you could sell at without losing money. It is worth calculating for every product you are considering, and it is covered in full in how to calculate your Amazon FBA break-even price.

Layer 4: ads, where per-unit models stop being true

Here is where most FBA spreadsheets quietly become fiction. PPC spend does not attach to a unit. It attaches to a month.

The cutting board’s month:

ACoS asks whether the ad campaign is efficient. TACoS asks whether the product still works once you accept that ads are a permanent cost of being on Amazon. Both belong on the tab, because a seller can hold a beautiful ACoS while TACoS climbs quarter after quarter — which is the signature of organic rank slipping and ads paying for sales you used to get free.

The number that decides whether an ACoS is good is your break-even ACoS, and it is simply your pre-ad margin: 41.4% here. Anything below that is profitable ad spend. That relationship, and what to do when a SKU’s break-even ACoS is 15%, is worked through in what a good ACoS is for Amazon FBA.

Layer 5: returns, the cost nobody models

Assume a 5% return rate. On 320 units that is 16 returns.

A returned unit does not simply reverse the sale. Using clearly-labelled assumptions — you have already paid the fulfilment fee, you have already paid the inbound shipping, and half of returned units come back unsellable:

That is $132.80 a month on one SKU — around $1,600 a year — sitting in no per-unit calculator anywhere. Log returns by SKU and by reason, because the reason column is the part that pays for itself: three returns marked “size too small” is a listing problem you can fix this afternoon, and it is cheaper to fix than to absorb.

Log reimbursement claims on the same tab with a status column. Amazon loses and damages inventory; the reimbursements are real money, and they only arrive if somebody is tracking which claims are still pending.

Layer 6: the roll-up, and the gap it exposes

Now put the whole month together for this one SKU. Assume the $39.99 Professional plan is spread across eight SKUs, so this one carries $5.00.

41.4% on the per-unit calculator. 34.5% in the bank. Seven points, on a product that is genuinely healthy. Run the same walk on a SKU calculating at 18% and the ads and returns take it under 10% — which is the moment you find out you have been buying inventory for the privilege of shipping boxes.

This is the entire argument for a monthly P&L tab that rolls up from the SKU rows rather than a one-off fee calculation. The per-unit number is a screening tool. The monthly roll-up is the truth.

Layer 7: inventory, where profit leaks silently

The last tab is not about fees at all, and it may be worth more than the rest combined, because a stockout costs you profit that no fee line will ever show you.

Four inputs per SKU — units in stock, average daily sales, supplier lead time, and the safety buffer in days — produce two outputs:

• Days of cover = units in stock ÷ average daily sales
• Reorder point = average daily sales × (lead time + safety days)

Take a second SKU from the same catalogue, a cork yoga mat: 180 units in stock, 7 sold a day, 35-day lead time, 14-day safety buffer.

• Reorder point: 7 × 49 = 343 units. You are at 180. You should have ordered three weeks ago.
• Days of cover: 180 ÷ 7 = 25.7 days. The replenishment takes 35.
• You will be out of stock for roughly 9 days.

At that SKU’s $17.09 net profit per unit and 7 units a day, nine days out of stock is about $1,077 of profit gone — plus the organic rank you spend the following month buying back through ads. A conditional format that turns a cell red when stock drops below the reorder point is the cheapest insurance in the workbook.

Making it a habit rather than a project

Three rules separate a spreadsheet you maintain from one you built once.

Log ad spend weekly, reconcile the whole sheet monthly. Weekly ad logging takes ten minutes and catches a campaign that has drifted; the monthly reconciliation against your payout report catches everything else. When the sheet and the payout disagree, the difference is nearly always a fee assumption you set months ago and never revisited.

Re-check size tiers after any packaging change. Not annually — after the change. A supplier who “improved” the box is the most common cause of a fulfilment fee that no longer matches the row.

Update settings before Q4, not during it. Storage costs more in the fourth quarter, which is exactly when your inventory levels peak, which is exactly when a stale storage assumption does the most damage to your planning.

Putting it together

The loop is short. Set your fee assumptions once in a settings tab → one row per SKU calculating referral, fulfilment, storage, margin and ROI → log ads and returns monthly → roll all of it into a P&L that shows what actually landed → let the reorder points tell you what to buy. The per-unit number tells you whether a product is worth selling. The monthly roll-up tells you whether it still is.

Two comparisons sit alongside this and are worth running before your next order: what Amazon FBA really costs per unit, fee line by fee line, and whether FBA or FBM is more profitable for a given product — a question that flips depending on the size and weight of what you sell.

You can build every tab above from the formulas in this guide. If you would rather start with it already built, that is what our calculator does.