Now Hold on a second!
forget the "depends on how you sell it" thing. As of 2019 unless you make over 25 million, you don't have to do inventory unless you want to or it just makes sense to. So, for a plumber, all material is inventory. ie, copper pipe, fittings, and fixtures, things bought at a Plumbing Supply House. We by it; it gets left at the place of installment; we get reimbursed for it. However, while I appreciate the flexibility, that we now don’t have to do inventory it gets confusing. Confusing because all things bought and eventually left and functionalized at a place of installment are material and now technically- legally- screws, joint compound, glue ect are supplies.
If then allowed, it is completely a dis-benefit to do inventory for a plumber because we buy a lot of material. Material that does not go into a job would sit on the property un-deducted- at a cost -until it's sold. So, unless you’re lucky enough to do a million and now 25 million, then expense it.
My problem with your answer is this: If one makes over a million, they shouldn't be asking you this question they would have an office team. so the answer is definitely for a guy or girl like me, on a budget and a self-doer. your answer is vague and everywhere I look on line this answer is continuously vague.
If you say "If you are using the supplies as part of a repair they would be entered in the expenses" and that's allowed, where is the section in Turbotax that says: this is where you enter material sold on a job, and here are examples. Some of the examples given on Turbotax, whether expensing supply house purchases or inventorying make me second guess what i'm doing.
Once again, if they are asking, then they don't make over 25 million. So, your advice should be: 1. don't do inventorying, and 2. here is how and this is where you enter it.
So Now the question: "Where do I enter the cost of material for a plumbing business that have already been sold? Is it supplies or inventory?" But now really, supplies or assets? this is what the original questioner should have asked and or you should have guided.
Supplies or assets?
I and we plumbers all have material bought and used, and then material bought and kept. while it is clear to deduct material bought and used it is not instructed well in Turbotax where to put it. As for bought and kept, asset or expense? If asset, once again, the examples make me feel like- no- but also do we have to really itemize every board and fitting and section of pipe. I would just like say Supply house 1. $1200 Supply house 2. $564 ect...
In Other word, since via advice on line and the IRS, I don’t have to do inventorying because we don’t make over 25 million, what then do I do with the money we lost this year sitting in the garage. No one says just exactly what to do since you don’t have to.
