Disadvantages of using a credit card on the last day of its expiration month

In a physical store the merchant should be running the card and the system should be validating the transaction. So if today in June 30th and the card expires this month the credit card company should validate the transaction, even if the final submission takes place after midnight. Of course that opens a discussion about when the day ends. Is it midnight local time or midnight someplace else?

A website should be doing the same thing. For something that is instantly delivered the approval process should lock the transaction. Typically there is a hold placed before an item is shipped, in cases when the delay is only a day or two that shouldn't be a problem.

Now in the case where there is a substantial delay between the reserving of a product or service, and the actual paying for it that is a different matter. This is a common occurrence when something has to be special ordered, or reserved far in advance. It isn't unusual in the case of airline tickets, hotel reservations, and the like. If I have a card that expires in 3 months, but my flight is in four months the airline knows the card will be replaced by then. They will block me from boarding the plane until I produce a replacement card, or another card. Hotels can do the same thing.

Of course even if the card doesn't expire I could decide to drop the card, or the bank could issue me a new card number during those 4 months. They will not know this until they try and complete the transaction.

I would expect some merchants might balk if the card is too close to the expiration date in a delayed transaction. They shouldn't have a problem if the transaction will either be completed at that exact moment, or shortly thereafter, because they will receive a validation code from the network.

Generally, No, it doesn't matter if you use your card on the last day of it being valid.

There may be some minor annoyances of doing so, which may include:

• If you later return an item in person, some stores require you to provide the card it was purchased with. It's possible you won't still have that card anymore, and (depending on how the store's card verification works) it's possible the new card would be considered different. If the new card doesn't work it may delay the return process, though I assume they could figure out how to refund it some way, and in the worst case I assume you'd at least get store credit (and if you know for sure you'd never use the store credit you may even be able to convince a manager to give you cash).
• If the card is not actually charged, but instead held, the charge may not go through in the future. Examples of this would be hotel bookings that charge the card 24 hours before you arrive, or out of stock items that charge you when they ship, etc. In my experience this isn't a big deal; sometimes it still works and when it doesn't you can just provide the new payment method if needed.

Side note, here are some interesting things I've experienced which may provide additional evidence that it normally shouldn't matter:

1. I've returned items, after my expiration date has changed, and also after my card number has changed (due to the previous number being compromised). In both of these cases the refunds went through to the account without issue. The point I mention above about stores sometimes requiring the physical card for a refund seems to be a store-dependent policy that only some stores have.
2. I've had subscriptions continue to successfully charge my account long after the expiration date has changed. (I don't know why some subscriptions keep working and others don't.)
3. I've had subscriptions continue to successfully charge my account even after the card number has changed. I have two recurring charges with Google, and after my card number was recently changed, when I went to update it in my Google account I didn't have to, because it had already auto-updated with my new card number! I don't know exactly how they did this without my knowledge, but apparently between Google and Citibank they worked it out.

All that being said, there are some situations where you may not want to risk a credit card getting denied, in which case I would recommend waiting until you know your new card details. For example, certain USCIS applications.