How much cash are you legally allowed to have on hand?

Is there actually a limit on how much cash I can just have? Like, stuffed under my mattress? I always wondered about that. Turns out, for carrying cash within the U.S., it's kind of a free-for-all. No limit, which is… wild, right? You could theoretically carry around a suitcase full of cash. (Though, honestly, why would you? Talk about a target.)

Now, traveling internationally is a different story. I remember this one time, my uncle was going to visit family overseas, and he was carrying a substantial amount of cash – a gift, I think. He nearly forgot to declare it! It was a close call. See, you absolutely have to declare anything over $10,000 (USD) when you’re going to or from the U.S. It’s not like they're gonna confiscate it (necessarily!), but you must declare it. Customs needs to know. So, word to the wise, if you're jet-setting with a wad of cash, don't forget that little detail! Could save you a lot of hassle.