How to Track Parts Inventory in an Auto Repair Shop
Master parts inventory management to reduce waste, improve margins, and ensure parts are available when you need them for customer jobs.
Parts inventory management is where many independent shops lose the most money. A part that sits on a shelf for a year is money tied up in inventory. A part you're out of when you need it forces you to order expedited, costing more. A part ordered twice because it's not tracked is waste. Proper inventory management recovers 10-15% of lost shop profit.
Why Shops Lose Money on Parts
A shop owner estimates that 40% of parts used are from stock. But 15% are customer-supplied (reducing your margin), 20% are ordered specially (no margin), and 25% are emergency orders at inflated prices. Without tracking, you can't distinguish between stock parts (good profit), ordered parts (no profit), and emergency parts (negative profit). You think you're at 40% parts margin when you're really at 20%.
Stock vs. Ordered vs. Customer-Supplied Parts
Stock parts are ones you keep on hand and use regularly. They should have the highest margin (40%+). Ordered parts are sourced for a specific job, often at lower margin (15-25%) because you're buying one unit. Customer-supplied parts have zero margin — the customer bought them and brought them in. Track all three separately so you know your true parts margin.
Set Reorder Points and Minimum Stock
For every stock part, set a minimum level (e.g., always have at least 3 oil filters in stock). When you hit that minimum, reorder automatically before you run out. This prevents emergency orders. Most suppliers offer volume discounts when you order 10 units instead of 1, so bulk ordering saves money too.
Identify and Clear Dead Stock
Some parts sit on your shelf forever — specialty filters for a car model you rarely see, old alternators that have been replaced by updated versions. These tie up cash. Quarterly, review slow-moving parts and either discount them to clear them or donate them for tax write-off. A $500 part sitting for 2 years is a sunk cost.
Build Strong Supplier Relationships
Negotiate volume discounts with your main supplier. Ask for extended payment terms (net-30 instead of net-15). Some suppliers offer consignment arrangements where you hold stock but don't pay until you use it — great for expensive items. A good supplier relationship saves 10-15% on costs through discounts and terms.
Mechanics links every part to a job and alerts you when stock hits reorder threshold — automatically suggesting reorder quantities based on your usage patterns. You'll never run out of a common part or order emergency stock again. Plus, you see which suppliers deliver consistently good parts and which generate comebacks, so you can adjust relationships for both cost and quality.
Ready to get organized?
Mechanics helps you track vehicles, manage work orders, and run a better shop — free to start.