Free calculators for Amazon and multi-marketplace operations
These free calculators turn your own numbers into an estimate for everyday operations decisions. Each one runs in your browser, needs no email, stores and sends nothing, shows its formula and tells you where to find each input. Results are estimates from your inputs, never revenue projections.
Stockout cost
Free Amazon stockout cost calculator: lost margin from daily units, days out of stock and unit margin, plus ad spend and recovery. No email, nothing stored.
Stockout cost = average daily units × days out of stock × unit contribution margin, plus the optional lines you enter: ad spend that kept running, margin lost while sales recover (daily units × recovery days × shortfall % × unit margin) and one-off restock costs
- Average daily units: Business Reports > Detail Page Sales and Traffic by Child Item: Units Ordered for a stretch when the SKU was in stock, divided by those days
- Days out of stock: Inventory Ledger, summary view aggregated daily and by country, filtered by FNSKU: days where the Sellable ending warehouse balance was 0, plus days until restock if still out
- Unit contribution margin: Selling price minus landed cost, referral and FBA fees (SKU Economics report or Profit Analytics) and other per-unit costs
- Ad spend that kept running (optional): Your ad accounts for the stockout dates: spend on campaigns that still sent shoppers to the listing
- Recovery days and shortfall (optional): Inventory Ledger by day after the restock: daily Customer shipments compared with your average before the stockout
- One-off restock costs (optional): Your freight, prep and inbound invoices: only the extra over your normal cost
- Average selling price (optional): Business Reports, same report and dates: Ordered Product Sales divided by Units Ordered
Agency vs in-house vs owned
Ecommerce operations cost calculator: three-year totals for an agency, an in-house team and an owned system, from your quotes and BLS pay. Formulas shown.
Three-year cost = year 1 + year 2 + year 3. Agency: the larger of retainer + % of sales + % of ad spend or the monthly minimum, plus tools, setup and the people you keep. In-house: wages ÷ (1 − benefits share other than paid leave), plus tools and recruiting. Owned system: build, yearly maintenance, hosting and licenses, plus the people you keep.
- Agency fees: The agency's proposal or contract: monthly retainer, any percentage of sales or ad spend, a monthly minimum and a setup fee
- Monthly sales: Seller Central Business Reports: Ordered Product Sales for the last three full months, divided by three. Add the other channels in scope from their own sales reports
- Monthly ad spend: The Spend column in Amazon Ads Campaign Manager for the same three months, divided by three. Count only the spend the agency's percentage applies to
- Wages: BLS May 2025 medians by default; replace them with your own offers or local pay data
- Benefits share, other than paid leave: BLS Employer Costs for Employee Compensation, June 2026, private industry: all benefits 30.0% minus paid leave 7.5% = 22.5%. Use your payroll provider's figure if you have one
- People in each model: Your org chart: who you would hire in-house, and who stays on your payroll with an agency or an owned system
- Build cost and maintenance: A written quote for the system: the one-time build fee and yearly maintenance or support as a percentage of it
- Hosting, licenses and tools: Your cloud invoices, the license terms in the quote and the subscriptions each model would still need
- Contribution margin after ads (optional): Monthly sales minus product cost, marketplace selling and fulfillment fees, returns and ad spend. On Amazon, the fees and refunds are in your Seller Central settlement reports; product cost comes from your books
Reorder point calculator
Free reorder point calculator for Amazon FBA: safety stock by service level, lead time split into supplier, freight and FBA check-in, and stock in all places.
Reorder point = average daily demand × (supplier + freight + 3PL receiving + transit to Amazon + FBA check-in days) + safety stock, where safety stock = z × √(lead time × σ of daily demand² + daily demand² × σ of lead time²)
- Amazon average daily units: Business Reports > Detail Page Sales and Traffic by Child Item: Units Ordered for a period, divided by the days the SKU was in stock
- Standard deviation of daily units: All Orders report (Reports > Fulfillment), requested by order date: add up quantity for the SKU per purchase date, remove stockout days, then STDEV in a spreadsheet
- Other channels on the same stock: Each channel's order report (Walmart, Shopify, TikTok Shop, wholesale) for orders filled from this SKU's stock
- Supplier, freight and 3PL receiving days: Your PO, ready, ship, delivery and 3PL receipt dates for recent orders on this supplier and route
- Transit to Amazon and check-in days: Shipping Queue > shipment summary > Shipment events tab: Shipped to Delivered for transit, Delivered to Receiving for check-in
- Standard deviation of the lead time: STDEV of the total days from PO to units available at FBA across your recent orders
- FBA available and inbound: Restock Inventory report: Available plus FC transfer, and Shipped plus Receiving (the FBA Manage Inventory report has the same inbound columns)
- AWD, 3PL and warehouse stock: AWD inventory in Seller Central, your 3PL's inventory report and your own warehouse count
- Open supplier POs: Your purchasing records: units ordered and not yet received
How do we build these calculators?
Every calculator uses a published formula and only the numbers you type. Nothing is stored or sent: the math runs in your browser. Where a calculator offers a default value, it comes from a public source that is linked and dated on the calculator's page. Each result is labelled "Estimate from your inputs" because that is what it is: real costs depend on data a calculator cannot see.
Want the real numbers from your account?
The free 24-hour diagnostic reads your Amazon account's data and reports what is going wrong within 24 hours of connecting, on business days. For the definitions behind each input, see the glossary; for the problems these numbers point to, see the operations gaps.
Frequently asked questions
Do you store or see the numbers I enter?
No. Each calculator runs entirely in your browser. Nothing you type is saved, sent to our servers or shared, and there is no email gate.
How accurate are the results?
As accurate as the inputs. Each result is an estimate from the numbers you enter and the formula shown on the page. It leaves out anything the calculator cannot see, which each page lists under what the result includes and leaves out.
Why do the calculators not project revenue?
A revenue projection reads like a promise, and no calculator can know how your market will move. These tools estimate costs and operations numbers from your own data, which you can check.
Want the real numbers from your own account?
Enter your email, connect your Amazon account with Login with Amazon, on Amazon’s own consent screen (we only read data; we never change listings, prices, stock or ads), and get a free report of what is going wrong within 24 hours of connecting, on business days. Prefer to talk it through? Schedule a call with the team that built these systems.
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