Amazon FBA ROI, Payback & Inventory Turnover Calculator

A profitable FBA SKU is not only about margin. Use this calculator to see whether your unit economics, cash payback and stock velocity work together before you reorder.

ROI + Payback + Turnover Inputs

Unit Economics
Referral Fee:$0.00
Landed Investment:$0.00
Profit Before PPC:$0.00
Pre-ad ROI:0.00%
Total Cost / Unit:$0.00
Profit / Unit:$0.00
Net Margin:0.00%
Monthly Revenue:$0.00
Inventory Investment:$0.00
Capital Velocity
Monthly Profit:$0.00
ROI:0.00%
Payback Months:0.00
Cash Conversion Days:0.00
Annual Inventory Turnover:0.00x
Monthly Sell-through:0.00%
Days of Inventory:0.00
Daily Unit Sales:0.00
Reorder Point Units:0
Target Stock Units:0
Suggested Reorder Units:0
Reorder Investment:$0.00
Post-reorder Coverage Days:0.00
Inventory Status:-
Recommended Action:-
Decision Band:-

What This Tool Measures

ROI alone can hide inventory problems. This tool combines per-unit profit, monthly cash recovery and inventory velocity so you can decide whether a SKU deserves a reorder, a smaller purchase order, or a pricing/PPC correction.

Formula and Logic

The calculator first builds landed investment from product cost, inbound shipping and prep. It then separates pre-ad profit from final profit so you can see whether PPC is the main drag. ROI = Profit per Unit / Landed Investment Γ— 100%. Pre-ad ROI = Profit Before PPC / Landed Investment Γ— 100%. Payback Months = Inventory Investment / Monthly Profit. Cash Conversion Days = Payback Months Γ— 30. Annual Inventory Turnover = Monthly Units Sold Γ— 12 / Inventory Units. Reorder Point = Daily Unit Sales Γ— (Lead Time Days + Safety Stock Days). Target Stock = Daily Unit Sales Γ— Target Coverage Days.

Example: $34.99 FBA Replenishable SKU

For a product priced at $34.99 with $12.00 supplier cost, $1.50 inbound shipping, $0.75 prep, 15% referral fee, $5.40 fulfillment fee, $0.45 storage and $3.00 PPC per unit: Step 1, landed investment is $14.25 and Amazon fees are $11.10. Step 2, final profit is $6.64 and ROI is 46.61%. Step 3, monthly profit is $1,992.45, payback is 4.29 months, annual turnover is 6.00x and days of inventory is 60. Step 4, with 10 daily sales, 45 lead-time days, 14 safety-stock days and 90 target-coverage days, reorder point is 590 units, target stock is 900 units and the suggested reorder is 300 units requiring $4,275.00 in landed cash.

Key Factors

  • Landed investment: High impact because every extra dollar in product, freight or prep lowers ROI and extends payback.
  • PPC cost per unit: High impact for launches; a $1 ad-cost increase can move a marginal SKU from reorder to watchlist.
  • Inventory depth: Medium impact; too much stock creates slow payback even when unit profit is positive.
  • Monthly sales velocity: High impact because turnover and days of inventory depend directly on sell-through.

Assumptions and Limits

This estimate includes supplier cost, inbound freight, prep, referral fee, fulfillment fee, storage allowance and PPC per unit. It does not model coupon redemptions, return loss, aged-inventory surcharges, taxes, currency movement or stockout risk. Check storage and landed-cost assumptions before placing large purchase orders.

Frequently Asked Questions About FBA ROI, Payback and Turnover

Why should I check payback period together with ROI?
ROI shows profit relative to landed investment, while payback period shows how many months it takes to recover the cash tied up in inventory. A high-ROI SKU can still strain cash flow if it takes eight or nine months to sell through.
What is a healthy inventory turnover rate for Amazon FBA?
Many private-label sellers prefer at least four to eight turns per year, depending on category lead time and margin. Faster turnover usually lowers storage risk and frees capital for the next purchase order.
Should PPC be entered as daily spend or cost per unit?
Use the PPC cost per unit field. Divide recent campaign spend by attributed units sold, or use ad spend per ordered unit when attribution is incomplete. This keeps ROI comparable across different sales volumes.
What reorder decision should I make from the result?
Scale when ROI is strong, payback is under three months and turnover is fast. Tighten the reorder quantity when the SKU is profitable but capital recovery is moderate. Fix price, ads, cost or velocity when ROI and turnover are weak.
How do lead time and safety stock affect this model?
Lead time and safety stock raise the reorder point. If current inventory is below demand during lead time plus the safety buffer, the tool flags reorder now and estimates units needed to reach the target coverage window.

Data Sources & Policy References

  • Amazon Selling on Amazon Fee Schedule 2026 Source
  • Amazon FBA Revenue Calculator and FBA Fees 2026 Source

Disclaimer: This calculator provides estimates based on publicly available data. Actual results may vary based on market conditions, competition, and platform policy updates. This tool is for educational purposes only.