📸 Full version with screenshots: https://tomi431.github.io/Tomi/2026/07/31/profit-calculator
Most sellers calculate profit in their head. Price minus cost minus FBA fee — "seems okay." Then they wonder why their bank account does not match their spreadsheet.
A proper profit calculator is not a spreadsheet. It is a formula that accounts for every cost line item, updated with live data, and applied consistently across every platform you sell on. Here is how to build one — and why the platform-specific differences matter more than most sellers realize.
The Full Cost Formula
For a product sold on Amazon via FBA, the actual cost per unit is:
Unit Cost =
Product Cost (1688 ex-factory price + shipping)
+ Amazon Commission (15% for most categories, varies by category)
+ FBA Fulfillment Fee (weight and size tier)
+ Monthly Storage Fee (per cubic foot, accrues daily)
+ Aged Inventory Surcharge (after 181 days)
+ Advertising Cost of Sale (total ad spend ÷ units sold)
+ Return Cost (return rate × per-unit return processing cost)
+ Inbound Shipping (sea/air freight ÷ units per shipment)
+ Customs/Duties (tariff rate × declared value)
Most sellers only track the first three. The rest are invisible until they show up in the monthly profit statement — by which point the money is already spent.
Platform Differences That Change the Math
The same product sold on Amazon, Walmart, and TikTok Shop has three different profit profiles. Here is why:
Amazon: Highest commission (15% for most categories). Highest FBA fees. Also highest traffic and conversion rates. The premium you pay for Amazon's infrastructure is offset by the revenue volume — but only if your margin can absorb the fees.
Walmart: Lower commission (8-15% depending on category). Lower fulfillment fees for WFS. Lower traffic but also lower ad CPCs. For products in the $15-40 range, Walmart often yields better unit economics than Amazon — fewer sales, but more profit per sale.
TikTok Shop: Commission varies by category (2-8%). No FBA equivalent — fulfillment is seller-managed or through TikTok's logistics partners. The wildcard is creator commission: if you work with affiliates, budget 10-20% of the sale price for creator payouts. The unit profit looks great on paper; the affiliate cost is the hidden variable.
# Pull live pricing and fee data:
# product_detail → current price on each platform
# category_report → competitive pricing benchmarks
# ali1688_similar_product → procurement cost validation
The FBA Fee Trap Most Sellers Miss
Amazon's FBA fee is not static. It changes when your product's dimensional tier changes — and Amazon measures and re-measures products automatically. A product that was initially classified as "Large Standard" can be reclassified as "Large Oversize" after Amazon's automated measurement system re-scans it. The fee difference can be $3-5 per unit — applied retroactively to your inventory.
Check your FBA fee reports monthly. If a product's fee changed without you changing the product or packaging, file a dispute with photographic evidence of the product's actual dimensions. This is a tedious task that an agent can flag for you — but you need to provide the evidence.
Automating the Calculation
The manual version: download reports from Seller Central, copy into a spreadsheet, update formulas, repeat monthly.
The agent version: your agent queries live pricing data, applies the cost formula, and outputs a per-ASIN profit dashboard. You set it to run every Monday morning.
The difference is not just time saved. It is accuracy. Manual profit calculations have errors — a forgotten fee, an outdated rate, a rounding mistake. An agent applies the same formula consistently every time.
Try it yourself: git clone https://github.com/DannylydST/sorftime-seller-agent → python3 scripts/install.py → get your key at open-intl.sorftime.com
Originally published with screenshots at https://tomi431.github.io/Tomi/2026/07/31/profit-calculator.
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