A reseller profit tracker turns scattered purchase records, marketplace fees, and inventory counts into decisions you can repeat. This guide explains how to build a practical spreadsheet for Amazon, eBay, Walmart, or Shopify, calculate landed cost and net profit, monitor sales velocity, set reorder points, and identify when changing fees or supplier pricing require a fresh review.
Overview
Reseller inventory management is more than counting units. You need to know what each item actually costs, how quickly it sells, how much cash is tied up, and whether the expected margin remains available after fulfillment, marketplace charges, returns, discounts, and other operating expenses.
A useful reseller profit tracker should connect four views:
- Inventory: what you own, where it is stored, and how many units are available, reserved, damaged, or in transit.
- Unit economics: the purchase cost, inbound shipping, preparation, fulfillment, selling fees, and other costs attached to one sale.
- Performance: units sold, revenue, sales velocity, days of supply, and realized profit.
- Cash flow: money paid to suppliers, money received from marketplaces, upcoming bills, and capital available for the next buy.
Keep product research separate from post-purchase performance. A product can look profitable during sourcing but produce a different result after actual sales, returns, discounts, and storage costs. Your tracker should preserve both the original estimate and the realized outcome so you can improve future buying decisions.
How to estimate
Start with a product-level calculation rather than a general store margin. Use one row for each SKU, variation, or condition that has a meaningfully different cost structure. A basic estimate is:
Estimated net profit per unit = selling price − landed product cost − marketplace fees − fulfillment cost − other variable costs
Landed product cost includes the supplier price plus the portion of inbound freight, handling, prep, customs, or other purchase-related costs assigned to each unit. If a shipment contains 100 units and has an allocated inbound cost of $80, add $0.80 to the product cost for each unit, assuming the allocation is appropriate.
Then calculate margin:
Net margin = net profit per unit ÷ selling price × 100
For a broader view, estimate the result for the planned buy:
Projected profit = estimated net profit per unit × expected sellable units
Use conservative inputs when the result depends on uncertain pricing or demand. You can create low, expected, and high scenarios by changing the selling price, sales velocity, return rate, or advertising cost. This is more useful than relying on one precise-looking forecast.
For inventory planning, calculate sales velocity using a consistent period:
Average daily sales = units sold during the review period ÷ number of days in that period
Then estimate days of supply:
Days of supply = available sellable units ÷ average daily sales
If sales are irregular, use a longer review period or mark the result as low confidence. Do not treat a short promotion or a one-time spike as a normal run rate.
Inputs and assumptions
A reusable spreadsheet can use separate tabs for SKU Master, Purchases, Sales, Expenses, and Dashboard. This structure reduces the risk of overwriting a product’s original cost when supplier pricing changes.
SKU Master
Record SKU, product title, brand, marketplace listing identifier, supplier, condition, storage location, reorder point, target margin, and any selling restrictions or documentation notes. If you source from wholesale suppliers for resellers, retain the supplier invoice or purchase reference alongside the SKU record. Documentation can matter when evaluating supplier reliability or resolving marketplace questions.
Purchases
Include purchase date, supplier, order number, units ordered, units received, unit cost, inbound shipping, prep cost, taxes or duties where applicable, and total landed cost. A simple allocation formula is:
Landed cost per unit = (product subtotal + inbound costs) ÷ received sellable units
Use received sellable units rather than ordered units when shortages or damaged items affect the effective cost.
Sales
Track sale date, SKU, marketplace, quantity, gross selling price, discounts, refunds, marketplace fees, payment processing charges, fulfillment charges, and any advertising or promotional cost assigned to the sale. Separate gross revenue from the amount actually paid out. A marketplace settlement may combine multiple orders and adjustments, so reconcile it against order-level records where possible.
Dashboard
Useful fields include on-hand units, units sold during the selected period, revenue, realized profit, realized margin, average daily sales, days of supply, inventory value at cost, and cash committed to open purchase orders. Add a status such as reorder soon, review margin, or pause buying to turn numbers into actions.
For a basic reorder point, use:
Reorder point = expected daily sales × supplier lead time in days + safety stock
Safety stock should reflect uncertainty in demand and replenishment. Keep the assumption visible rather than hiding it inside a formula. A product with unreliable lead times may need a larger buffer, while a seasonal or highly volatile product may require manual review instead of automatic replenishment.
Worked examples
Example 1: Comparing estimated and realized profit
Assume a reseller buys 40 units at $12 each. Inbound shipping and preparation total $40, so the landed cost is ($480 + $40) ÷ 40, or $13 per unit. The item sells for $29. The reseller estimates $6 in marketplace and fulfillment costs per unit and sets aside $1 per unit for expected discounts or related variable costs.
Estimated net profit per unit is $29 − $13 − $6 − $1 = $9. The estimated margin is $9 ÷ $29, or approximately 31%. If all 40 units sell under those assumptions, projected profit is $360 before fixed overhead, income taxes, and costs not assigned to each unit.
After the sales period, the tracker shows that several units sold with discounts and the realized average selling price was $27.50. Actual variable costs averaged $7.25 per unit. Realized profit becomes $27.50 − $13 − $7.25 = $7.25 per unit. The difference does not necessarily mean the product was a failure; it shows which assumptions need to change before the next purchase.
Example 2: Setting a reorder review
A SKU sold 36 units over the last 30 days, giving an average daily sales rate of 1.2 units. The supplier’s typical lead time is 14 days, and the reseller chooses safety stock of 10 units. The reorder point is 1.2 × 14 + 10 = 26.8, which can be rounded to 27 units for operational use.
If 25 sellable units remain, the tracker should flag the SKU for review. That does not automatically mean placing an order. First check current margin, supplier availability, cash flow, listing health, seasonality, and whether the recent sales rate was representative.
When to recalculate
Recalculate the product economics whenever a pricing input changes. This includes supplier cost, inbound freight, fulfillment charges, marketplace fees, payment processing, shipping supplies, advertising allocation, discounting, or return-related costs. Do not wait for month-end if a single change materially affects a high-volume SKU.
Review sales velocity and reorder points on a regular operating rhythm, such as weekly for fast-moving items and less frequently for slow-moving inventory. Revisit the assumptions after a promotion, a major listing change, a new supplier, a seasonal transition, or a period of unusual demand.
At least once each reporting period, reconcile the tracker with marketplace settlements, supplier invoices, inventory counts, and bank activity. Investigate differences rather than forcing the spreadsheet to match. Common causes include unrecorded returns, damaged stock, receiving shortages, duplicate purchase entries, or fees posted after the original order.
For practical next steps, create the five tabs described above, enter a small group of current SKUs, and compare estimated profit with realized profit from completed sales. Then set a reorder point only for products with reliable sales and documented costs. If you use a dedicated platform, compare its features with your spreadsheet requirements in this guide; a system is valuable when it preserves accurate inputs and makes exceptions easier to act on. See the guide to inventory management software for resellers for considerations when evaluating tools. For sourcing decisions, pair the tracker with research on profitable products to resell online and a wholesale supplier verification checklist. The goal is not a perfect forecast; it is a current, traceable view of where inventory cash is going and what it is returning.
