You’re making an uncharacteristic stop at a jewelry store to buy a costly gift for your great-aunt’s 80th birthday when your credit card is rejected. Why? Depending on the issuer’s fraud-fighting program (some are very sensitive) and the time of the year (banks tend to be more lenient during the holidays), the reasons vary. Here are the most common.

Account delinquency. If you habitually pay late by 30 or more days, the bank could restrict your charging privileges.

Geographic location. Go outside your normal area and you could end up with a card that won’t work. Traveling overseas? Avoid a sticky situation by giving your credit-card issuer a heads-up.

Suspicion of fraud. A credit issuer may suspect your card has been stolen if there’s a notable change in your shopping patterns — for instance, your card comes up as having made huge buys at Saks and Neiman Marcus, but you’re the Target type.