While I expect most women buy in advance, I expect they also don't buy enough and so are out there mid-period at least some of the time. Their cycles also affect their buying patterns, so even women who are stocking up are more likely to buy differently in different parts of the cycle.

The real question is what does the manager do with the data. Across a city on any given day there are about the same number of women in every day of their cycle so it isn't like they are marking up pads on the 25th-28th day of the month to get women who didn't stock up. As such I don't think this data is useful, what is useful is when they discover a women missed her cycle and thus needs to get ads for pregnancy wear in a couple months. Since that is their need for data, the fact that it is noisy and not very accurate is still close enough.

That said, they probably are more accurate than you would expect despite all the noise. Not 100% accurate, but being greater than 50% accurate is a lot better than chance and should be obtainable.

You think the data brokers aren't aware of varying spending habits? You might be surprised to learn the number of people living day-to-day, cheque-to-cheque who don't have the ability to stock up on much of anything. These are the consumers who are "ripe for the picking" in marketer's eyes. Back in the late 90's this would have been much harder too, probably working with not much more than cash register receipts.

You're making a lot of assumptions there. The guy probably had a training dataset with real cycle data and shopping data and went off of that.

> Because even with hygiene products, people buy them before they need them and stock up.

One would think so, but in my experience this is not the case on average. Of the half-dozen long term relationships I've had, only 1 partner was ever prepared for the monthly inevitable. For everyone else it was always treated as a surprise. Suggesting to my current partner that she stock up on the products she just used was dismissed with an "oh I don't need that stuff for weeks".

The trope of guys not wanting to go get tampons, or uncomfortably navigating the feminine hygiene isle, did not just appear out of nowhere.

From an advertising POV, isn’t that even better? Then they’d know when to advertise to someone to increase sales.

That is, the marketers wouldn’t actually care about a woman’s cycle, but at which points they could monetize it.

(Good lord, I need a shower after just typing that.)

I think it's more about when to push than about what to push. Maybe there are specific types of products aside from what's obvious, or actions to take or not to take. Like avoiding discounts when customers are least likely to develop loyalty, maybe even how to rotate through choices of products like meats to vegs to dish soaps.

By the way, I've seen self proclaimed male on social media posting how they use these trackers to predict their irresistible sushi cravings. Apparently, and contrary to intuition, men also have the cycle, just less obvious. Pelvis opening up and such.

They don't care about your menstrual cycle. Advertisers want to predict your purchase pattern to better target you. So, what you said just reinforces the idea that using menstrual cycle data for placing ads is useful. Essentially using your body against yourself.

> And with food, you're often shopping for a week

That’s not how people shop here in Europe

I don't tend to keep candy in the house. You could track my youngest daughter's menstrual cycle pretty accurately by how often I buy Hershey's bars with almonds. They are never consumed in our household other than during the first part of a particular week. My older daughter and wife don't have quite the same tells though.