SHOP SUPPLIES FEE CALCULATOR

What the fee is supposed to cover

Solvents and cleaners, small quantities of fluid, rags and their laundering, servicing the parts washer, and the disposal of used oil, coolant and other regulated waste. What ties them together is that metering them per job would cost more than the consumable. That is the honest argument for a blanket fee, and it is a good one.

Percentage of labor, with a cap

The common convention is a flat percentage of the bill — 7 or 8 percent in Car Talk's example. Labor is the right basis because consumable use tracks hours in the bay, not the price of the part being fitted. A $2,400 catalytic converter uses no more brake cleaner than a $200 one.

The cap is what keeps the fee honest on a long job. Without it, a 12-hour engine job carries a $100 supplies line that no reasonable accounting supports.

The rules vary by state

Some states restrict the fee to actual cost with no markup; some require it to be disclosed in writing before authorisation; some require every charge on a repair invoice to be itemised, which means a bare “shop fee” line is not compliant. Check your own state’s rules before you set the percentage, and put the disclosure on the repair order where the signature is.

Where it lands on the paperwork

The estimate calculator applies the same percentage-with-a-cap logic, so a customer who compares the estimate against the invoice sees the same number twice — which is the point. If the fee is doing real work in your margin rather than covering real consumables, that is a door-rate problem wearing a disguise.