What to actually stock
The rule: stock what you repair every week; order on demand what you repair once a month. For most phone repair shops that means screens and batteries for the popular models (the top Apple and Samsung devices you actually see), charging ports, and the accessories you sell at the counter. For computer shops: SSDs, RAM, universal chargers, keyboards.
Resist stocking broadly "just in case" — a part for a rare model that sits on the shelf for a year is trapped cash, and often a depreciating one.
A reorder point for every item
Give every item a minimum quantity that triggers a reorder. The math is simple: weekly usage × supplier lead time in weeks + one unit of buffer. An iPhone screen you use twice a week with a one-week supplier: reorder at 3. Without a reorder point, ordering happens only when someone finds an empty shelf — which is by definition too late.
The key principle: inventory linked to repairs
Manual stock counts are always wrong for one reason: consumption isn’t recorded the moment it happens. The fix is linking inventory to the work itself — when a part goes onto a repair ticket, the quantity drops right then. That way the record always mirrors the shelf, and the monthly count becomes a quick verification instead of a reality check.
Cost vs price — your real margin
Record the purchase cost of every part alongside the customer price. Without it, "a $90 repair" sounds profitable even when the part cost $62 and the job took an hour. With cost on every part, you can see true margin per repair type — and often discover the "small" repairs are the truly profitable ones.
Parts that are whole devices
Refurbished phones and trade-in units are a different kind of stock: every unit is unique, with its own IMEI and its own condition. You don’t count those as a quantity — you track each unit individually: received, reserved for a customer, sold. If you sell refurbs, make sure your system (or your process) can track that way too.