Alex,
Doesn't this sound like Rick's ubiquitous "QTY on hand" numeric fields. Your unit of sale for these items is something like "prepaid usage events remaining" and not physical inventory units available for sale. I would follow his inventory tracking model used throughout the early lessons of his Access Series with this difference in mind.

Hi Alex

You will find what you are looking for in the following:
Access Developer 19 lesson 5
Access Developer 23 Lesson 1-5

good luck

Yes, it's a prepaid usage.

Thanks for your advice.

Yeah, I would probably just use a single field for this to determine how many times they've used it or have uses left. So, if they buy 10 and they've used three, then this value would be 7. And then, if you want to track the specific rentals, the specific usage is just to make a second table, very much analogous to my contact table. Every time they use it, put a note in there in the contacts. It'll have the date and then you can keep track of it that way.

Now, if you had a situation where you had multiple products that they could rent, so in addition to bikes, you had motorcycles, jet skis, and pontoon boats, then you might want to look into a situation where you have an inventory in/inventory out system. Every time they purchase a rental, it adds to their quantity for that particular product, and then when they return it, it subtracts that quantity. You can do something like this with a product ID and maybe just a query that adds all of the particular products up. So, every time they rent one, you put a negative quantity in that field, and then by adding up all the positives and the negatives, you'll get their balance. There's lots of stuff you can do. There are tons of different ways to do this. It's all a matter of how you want to put the Legos together.

This would actually make for a pretty good TechHelp video. I'm going to add it to the list. The list is quite long at this point so if you're in a hurry get those other lessons LOL.

Yes, guys. This is what I find so appealing about working with Access. There are few limits to creating information systems to monitor the vital signs of our enterprises in real time. This kind of "inventory" is unique in that it moves both in and out of our warehouse. Even a modest collection of such will require a substantial initial investment and in addition to warehousing costs there must also be maintenance and replacement expenditures. Eventually, the database can track any movement under the roof. Like a lemonade stand where customers must rent the expensive cups.