Most reorder emails go out on one schedule: thirty days after the purchase, whatever was bought. Products don’t run out on one schedule. A reminder that arrives while the bottle is still half full gets ignored, and one that arrives after it is empty arrives after the customer has already decided where to buy the next one.
The arithmetic is simple
How long a product lasts is its size divided by how much of it is used in a day. A 50ml moisturizer used at about 1.1ml a day lasts roughly 45 days. A 30ml serum used at about half a millilitre a day lasts roughly two months. Those two products, bought in the same order, want reminders about two weeks apart, and neither wants one on day thirty.
The daily amounts are estimates for a category, not measurements of a person. They are a starting point, and they should be treated as one.
Two clocks, not one
The size and the category give you the product’s clock. The customer has a clock of her own: the gap between her orders of the same thing. Someone who has bought the same serum four times, about every forty days, has told you more about her own use than any category average can.
So the product’s clock is what you use when there is nothing else, and the customer’s own interval takes over once there are orders to read.
Remind before it runs out, not after
The useful moment is shortly before the product is finished. Altvary treats a product as due from a week before its estimated run-out. Earlier than that and there is no reason to act; later and the reminder is describing a problem the customer has already solved.
Some products can’t be timed, and that is fine
Not everything in a catalog has a dependable run-out date. Three cases come up again and again:
- No size on the listing. Without a size there is nothing to divide. Adding it to the product is the fix.
- No dependable daily use. Most makeup, for example. How fast a lipstick goes depends on the person far more than the product.
- Kits and sets. Several products in one box run out at different times.
For these, the honest answer is no date at all. A reminder timed from a guess is worse than no reminder, because it teaches the customer that your reminders are not about her.
See it on your own catalog
The free store check reads the public product list of any Shopify store and shows which products can be timed, roughly how long each lasts, and how a fixed reminder compares. It needs no account and nothing installed.