Amazon FBA profit math: every fee between $12 and $29.99

The most common mistake I see with new arbitrage sellers is simple. They take the Amazon price, subtract what they paid on the shelf, and call the difference profit. A $12 item selling for $29.99 looks like an $18 win. It almost never is.

Between the shelf and your bank account there are six or seven separate costs, and some of them only show up weeks later. This post goes through each one, then runs a full example so you can see where the money actually goes. I'll keep the numbers simple and I'll say clearly when they're made up for illustration.

One warning first. Amazon changes its fees often, sometimes more than once a year. Treat every percentage here as a rough guide and check Amazon's current fee pages in Seller Central before you buy anything.

The cost stack, one layer at a time

Buy cost, including sales tax. If the sticker says $12 and your local sales tax is 8%, you paid $12.96. People forget the tax all the time, especially when they buy in bulk. If you have a resale certificate and the store accepts it, you may not pay tax, but don't assume that.

Referral fee. This is Amazon's commission on each sale. It's a percentage of the total sale price (not your profit), and for a lot of categories it's around 15%. Some categories are lower, some are higher, and a few have tiers that change above a certain price. There's also a minimum referral fee per item in many categories, which hurts cheap products more than you'd think.

Closing fee. Media items like books, DVDs and video games carry an extra per-item closing fee on top of the referral fee. If you don't sell media you can mostly ignore this one.

FBA fulfillment fee. This is what Amazon charges to pick, pack and ship your item to the customer. It depends on the size tier (small standard, large standard, oversize and so on) and the shipping weight. A light, small item might cost a few dollars. A bulky one can eat a huge part of the sale. Measure the box, not the product inside it.

Storage. Amazon charges monthly storage based on cubic feet, and the rate goes up in the busy months near the end of the year. Items that sit too long can also get hit with long-term or aged inventory surcharges. Slow sellers quietly get more expensive every month they stay in the warehouse.

Inbound shipping and placement. You pay to ship your boxes to Amazon. Depending on how you split shipments, there may also be an inbound placement fee. On a per-unit basis this is often small, but on heavy items it adds up.

Prep and labeling. FNSKU labels, poly bags, bubble wrap, suffocation warning stickers. If you do it yourself it's your time plus materials. If you use a prep center it's a per-unit fee, usually somewhere under a dollar or two depending on the work.

Returns. Some customers will send things back. In some categories Amazon also charges a returns processing fee, and returned items sometimes come back unsellable. I like to set aside a small amount per unit for this rather than pretending returns don't happen.

A worked example (illustrative numbers)

Say you're in a store holding a kitchen gadget priced at $12. On Amazon it sells for $29.99. Here's how the full stack might look. These numbers are made up for illustration. Your real fees will depend on the category, size, weight and the current fee schedule.

So the "$18 win" is really about $5.63. Still a decent flip, honestly. But it's a very different picture, and if the FBA fee had been a couple of dollars higher or the price dropped to $25, it would be borderline.

Margin and ROI are not the same thing

These two get mixed up constantly, so here's the difference in plain words.

Margin is profit divided by the sale price. In the example, $5.63 out of $29.99 is 18.8%. It tells you how much of each sale you keep. Margin matters when prices drop, because a thin margin disappears fast if another seller undercuts you by two dollars.

ROI (return on investment) is profit divided by what you spent to get the item. In the example, $5.63 on a $12.96 buy is 43.4%. It tells you how hard your cash is working. Arbitrage sellers usually care about ROI more, because their limit is cash, not shelf space.

Some people put prep and inbound shipping into the ROI denominator too. That's fine, just be consistent. With those included, the same deal is $5.63 on $14.06, which is 40.0%. Neither number is wrong. Mixing the two methods between deals is where people fool themselves.

Demand: BSR and monthly sales

Profit on paper means nothing if the item doesn't sell. The main signal people use is Best Sellers Rank (BSR). Lower is better. A BSR of 5,000 in a big category usually means steady sales, while 800,000 might mean a sale every few weeks, or less.

The catch is that BSR is relative to its category and it moves hour by hour. One sale can make a slow item look hot for a day. I prefer looking at a rough estimate of monthly units sold and at the price and rank history over a few months, if you have access to it. A product that sells 300 a month split between 20 sellers is not the same as 300 a month split between 3.

Competition and risk

Number of FBA sellers. More sellers means you get a smaller share of the buy box, and it often means someone will start a price war. Look at how many are on the listing and how close their prices are.

Amazon on the listing. If Amazon itself sells the product, be careful. Amazon often holds the buy box, and it can match low prices for a long time. A lot of sellers simply skip these.

Gated brands and categories. Some brands and categories need approval before you can list. If you buy 30 units and then find out you're not allowed to sell them, that's a painful afternoon. Check before you buy, not after.

IP complaints. Some brands file intellectual property complaints against resellers, even when the product is genuine. Too many complaints can put your account at risk. Over time you learn which brands to avoid, and I'd rather lose a good-looking deal than gamble an account on it.

Rules of thumb people use

You'll hear a lot of thresholds in seller groups. The common ones go something like this:

• At least $3 to $5 profit per unit after all fees.
• An ROI of 30% or more.
• A BSR that suggests the item sells within a reasonable time for its category.
• Avoid listings where Amazon is selling, or where the seller count is very high.

These are rules of thumb, not advice, and I'm not a financial advisor. They exist because small mistakes in the estimate (a fee change, a price drop, a return) can wipe out a thin deal. A 30% ROI leaves room for being a bit wrong. A 10% ROI doesn't. Your own numbers depend on how fast you want cash back, how much you have to spend and how much risk you can live with.

Where Scout fits

I built Scout because doing this stack on a phone calculator in a store aisle is slow and easy to get wrong. You scan the barcode or enter an ASIN, it estimates profit after the referral, fulfillment and closing fees, and shows BSR, a monthly units sold estimate, the seller count, who has the buy box and whether Amazon is selling. Then it gives a FLIP, RISKY or SKIP verdict.

I'll be honest about the limits. These are estimates. Fees change, prices move, and the monthly sales number is a guess based on rank, not data from Amazon's books. Use the verdict as a quick filter so you can put back the obvious losers, then double check anything you're about to buy a lot of.

If you also sell on Walmart, the math there has its own quirks, especially around shipping. I wrote that up in Walmart reseller profit math.

If you only remember one thing: profit is what's left after every layer, not the gap between two price tags.