Inventory shrinkage is the gap between what your records say you should have in stock and what you actually have on the shelves. The formula is straightforward: subtract your physical inventory from your book inventory, divide by book inventory, then multiply by 100 to get a percentage.

Book inventory is what your accounting system shows based on purchases minus recorded sales. If you bought 500 units this quarter and your POS shows you sold 350, your book inventory says 150 should remain. Physical inventory is what you actually count when you walk the store and tally every item on the floor and in storage.

Here’s a practical example. Your records show $45,000 in merchandise should be on hand. You conduct a physical count and find $42,750 worth of inventory. The difference is $2,250. Divide $2,250 by $45,000, multiply by 100, and your shrinkage rate is 5%.

That 5% number should concern you. The National Retail Federation reports average retail shrinkage around 1.4% to 1.6% annually. Anything consistently above 2% deserves investigation.

Shrinkage comes from four primary sources: employee theft, shoplifting, administrative errors, and vendor fraud. Administrative errors often surprise business owners because they aren’t actual theft. Receiving shipments without verifying quantities, scanning the wrong item at checkout, or miscounting during inventory all create phantom shrinkage that looks like loss but is really just bad data.

To calculate shrinkage accurately, your book inventory needs to be right. That means recording every purchase at actual cost, tracking markdowns and damaged goods, and reconciling sales daily. If your book inventory is already wrong, your shrinkage calculation won’t tell you much. A Scottsdale bookkeeper who understands retail can help you get your records in order so your numbers mean something.

Physical counts should happen at least annually, though quarterly or monthly cycle counts catch problems faster. Waiting a full year to discover shrinkage means you’ve been bleeding money without realizing it.

Track shrinkage by category if you can. Your overall rate might be 2%, but if most losses come from one product line, that’s where you focus. High-value small items typically have the highest shrinkage rates because they’re easy to pocket and hard to notice missing.

Once you know your shrinkage rate, you can weigh prevention options against actual losses. Better security cameras, improved receiving procedures, or more frequent counts all cost money. Compare those costs to what shrinkage is actually costing you before investing.

Proper inventory accounting makes shrinkage calculation reliable. When your books accurately reflect what you’ve purchased, sold, and have on hand, the physical count becomes a meaningful comparison instead of a guess.