Why Your FBA Numbers Look Wrong and How to Fix Them
I spent three years dealing with Amazon FBA inventory discrepancies before I started building proper tracking systems. The issue wasn't Amazon's fault most of the time. It was sloppy record-keeping on my end. Once I committed to a comprehensive logbook approach, the whole picture changed. Revenue calculations became accurate, fee audits got easier, and I stopped losing sleep over missing shipments. A comprehensive FBA logbook is a structured tracking system that covers every aspect of your Amazon Fulfillment by Amazon operations. It records inbound shipments, receives, returns, refunds, fees, profitability per SKU, and customer service issues. Most sellers use a mix of spreadsheets and Amazon reports. A proper logbook ties them together so you're not cross-referencing five different tabs at 11 PM trying to figure out where $400 went. The standard columns you'll need include shipment ID, ASIN, SKU, units shipped, units received, date sent, date received, cost of goods sold, selling price, FBA referral fee, FBA fulfillment fee, storage fee, any removed or discarded units, return reason, and net profit per unit. That's the baseline. The people who take this seriously add columns for advertising spend per SKU, damage claims filed, and whether items were aged inventory or new stock.
I built my first logbook in Google Sheets. Simple, shared access, works across devices. I switched to Airtable six months later because the spreadsheet was hitting limits with 8,000+ rows and multiple linked tables. If you're just starting out with a small catalog, Google Sheets is fine. When you cross 200 active SKUs, consider something with relational capabilities. The time you save on lookups pays for itself quickly.
How to Set Up the Tracking System
Start by exporting your Amazon reports. You need the Manage Inventory report, the Shipment Details report, the Received Inventory report, the Transaction Overview report, and the Fee Preview report. Download them all for at least the last 90 days. This gives you historical context before you start fresh logging. Create a master SKU table with your cost price, supplier information, reorder point, and current selling price. This is your single source of truth. If you change the cost price in this table, every calculation downstream updates automatically. Don't edit cost prices in your shipment logs. Edit them in the master table and let your formulas pull from there. The biggest mistake I see people make is not accounting for returns at the time of sale. I used to log returns separately months later, which made my monthly profit calculations impossible to reconcile. Now I create a returns tracker that auto-populates from your Transaction Overview report. It captures the return date, reason code, refund amount, and whether the item came back to sellable inventory or got disposed. This alone cut my end-of-month reconciliation time from about four hours down to roughly thirty minutes.
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Common Pitfalls and What Actually Works
Amazon's reports don't always align with each other. The Shipment Details report might show you sent 120 units but the Received Inventory report shows 117. That's normal. Three units could be lost in transit, damaged at the fulfillment center, or still in processing. Your logbook should flag these discrepancies immediately rather than pretending they equal out by magic. I created a "discrepancy column" that subtracts received from shipped and color-codes anything over zero in yellow. Yellow means investigate. Red means it's been open for more than 30 days and needs a claim filed. Storage fees are another area where people lose money without knowing it. Amazon charges monthly inventory storage fees based on cubic feet. The rates change quarterly and vary between standard and oversized items. My logbook includes a storage cost column that references the current Amazon fee schedule. I update it manually every quarter when the rates change. Some sellers build this into their sheets with a lookup table tied to the current date. That works too if you're comfortable with INDEX-MATCH or XLOOKUP formulas. Here's something most guides won't tell you: advertising spend allocation. If you're running PPC campaigns across multiple ASINs, attributing ad costs to individual units sold matters for real profit calculation. I started using a simple algorithm where daily ad spend gets divided proportionally by units sold per SKU. It's not perfect but it's close enough for decision-making. The alternative is guessing whether a SKU is actually profitable after ads, which is worse.
Edge Cases You'll Hit
Last year I had a shipment of 340 units arrive at a fulfillment center with a barcode scanning error. Amazon's system recorded 312 units received. My logbook showed 340 shipped with a discrepancy flag in yellow for four weeks. I filed a reimbursement claim and got nothing back for two months. The workaround was to export the Reimbursements report weekly and cross-reference it against my discrepancy column manually. Amazon's automated reimbursement system misses a lot. I ended up recovering about 60 percent of the eligible claims that way, which added up to roughly $2,800 over six months. Another edge case involves liquidated inventory. If you remove excess stock and sell it through liquidation, that money shows up in your account but doesn't tie cleanly to your original cost basis in most export reports. I created a separate tab for liquidation recoveries that tracks the recovery amount against the original COGS. Without this, your profitability numbers are inflated because the recovery income isn't being netted against the actual loss on those units.
What This Approach Doesn't Fix
A comprehensive logbook won't prevent Amazon from making errors. It won't stop your suppliers from shipping the wrong quantity. It won't predict when a product will get suppressed from search. What it does is give you accurate data fast enough to act on it. That's the real value. Most sellers drown in raw data but starve for insight. A good logbook flips that equation. If you have under 50 SKUs and ship infrequently, a full logbook might be overkill. A basic spreadsheet with inbound and outbound tracking will serve you fine. The comprehensive approach is worth the initial setup time when you're moving more than 500 units per month across multiple ASINs. Below that threshold, the overhead of maintaining detailed records probably isn't justified by the ROI. I've tried several commercial solutions alongside my custom logbook. Inventory Lab handles some of this well but costs money per month and locks you into their ecosystem. Sellbrite and other multi-channel tools add complexity you don't need if you're purely FBA. For most sellers I talk to, a well-structured Airtable database or a properly built Google Sheet with linked tabs is the sweet spot between capability and cost.
