My deodorant expired. I noticed that over the course of a couple of weeks, the antiperspirant in my deodorant wasn’t working nearly well enough. Is it possible that antiperspirants have an expiration date? Is that even a thing for a bunch of chemicals? Well, yes. Turn over your roll-on or stick. You will likely see an expiration date of the form MM/DD/YYYY.

This use of the exact date for a product’s demise has always made me laugh: The baking soda will work perfectly on Monday, December 22nd, and will be ineffective on Tuesday, December 23rd, just when you’re about to make a last-minute batch of holiday cookies? I take a precaution and repurpose the baking soda to be a gentle scouring option at least a month before it will suddenly stop working as a leavening agent. I learned about baking soda expiration the day my biscuits didn’t rise. When a package of dry yeast shows an expiration date, take that seriously. I have a similar rule of thumb: Chuck it a month before that date. Yeast may be dormant as it chills in your refrigerator, but it is a living thing that does not live forever.

The gradual appearance of a less dire term for product failure dates has become “best by.” They’re not saying it will entirely fail on that date, but they’re warning you to get ready. A best-by date on whole wheat flour is telling you that the fats in the whole grains may be headed toward a rancid state. The exact date? Depends on how it’s stored and how long it’s been since the bag was first opened. Use at your own health risk on or about 8/12/2022.

What are we to make of sell-by dates? We’ve all noticed this date on one end of a carton of eggs. While there is some variation based on the state of origin of the eggs, the usual requirement is that the date cannot be any later than 30 days after the eggs were laid, cleaned, and packaged. How long will it be, then, before the eggs should not be used? Again, it all depends on the regulations of that region. The USDA recommends using the eggs within three weeks of that sell-by date. Or you could see if the eggs float in cold water. (They should sink and, if they don’t, they should be placed in the food waste bin.) One thing the regulations are consistent about: Don’t buy eggs that have passed that date stamped on the end of the carton. Sometimes grocery stores lose track of the day the carton should be removed from its refrigerated location, so never assume.

Here’s one place where I use month, day, and year: when putting food in my freezer. Some food seems to disappear for a very long time, having fallen below less-aged ingredients. Freezer burn is not what you want to rely on as a use-by date. Another time I use a complete date: when putting leftovers in the refrigerator. Cook the chicken on 3/17/2021? Place it in a sealable container and write the use-by date on the piece of freezer tape, using a permanent marker: 3/20/2021. Or adjust for whatever degree of risk you’re willing to take. I once lost an opened container of black olives in the back of my refrigerator for over a year. I’m not proud of it, but it happened, even though it had my personally chosen use-by date clearly written on the freezer tape.

Finally, there’s the personal choice of a toss-by date. For me, this is more of an intention than it is an adhered-to execution date. If I haven’t opened a file for a year, chances are very good that it can be tossed. That is, unless the file contains information used to fill out income tax forms. In the United States, keep those papers for three years from the filing date.

I’m not sure I should have purchased a two-pack of deodorant. What if the second one has an expiration date that’s sooner than I’m likely to finish with it? At least I now know to check. The container says 03/2023. I think that’s what it says, but the last digit is only partially visible. Fall-back plan? Notice when it’s no longer working.