When a flight attendant slaps a customs declaration form across your seat-back tray on your flight back to the U.S., you might know the general items you must declare — but do you declare that flashy Swiss watch you bought? What about those Italian earrings in a travel case in your carry-on? Customs regulations are confusing and knowing what and when to declare can be tough, but as the U.S. Customs and Border Protection Agency says on its website, "If in doubt, declare it."

In America, It's a Must

If you bought a watch or expensive jewelry while you were abroad you must declare it, even if it’s from a nearby country like Canada. However, that doesn't mean you have to pay taxes on your items. Most travelers qualify for CBP exemptions. If you traveled to anywhere other than Guam, American Samoa or the Virgin Islands, you will likely qualify for an $800 exemption. If you landed in one of those three U.S. insular possessions, you might qualify for a $1,600 exemption, but you still have to list any pieces of jewelry you purchased while abroad.

Declare It Abroad

The rules for what you must declare at customs abroad will vary by country, but the general rule still works: better to declare it on the CBP form to avoid confusion or hang-ups. Of course, you won't need to declare items from home, but if you're bringing in several Rolexes, Omegas, or necklaces as gifts or for other personal use, you're probably better off declaring what you have. Remember that you should declare any watches or jewelry you buy while abroad, even if you plan to wear them home.

Get Registered

You'll likely want to bring some personal items, such as fine jewelry or a nice wristwatch, on your trip, and some of the most expensive of these can be foreign-made. If you're worried about getting through U.S. customs with foreign-made timepieces or jewelry you brought with you when you left the states, you can register them at a CBP office or to a customs officer in the airport from which you're departing. In fact, customs officials recommend this practice to avoid confusion. You'll need the items and their serial numbers to fill out the registration forms.

Considerations

Declaring items even when you're unsure can save you money. If you don't declare an item that requires it, the fine you could incur would likely be much higher than the small tax you would have had to pay if you exceeded your exemption level. Don't forget you should always declare watches and jewelry you obtained abroad, even if they're for your business, from duty-free shops or gifts you received. The duty-free status of items you purchase in duty-free shops only applies in the foreign country in which you purchased them, so you might have to pay duty on these items in usd if their value exceeds your personal exemption.

As for things like gold coins and bullion, you will have to estimate their value on your declaration forms. With items made from precious metals, aim for a reasonable estimation that won't draw attention for being too low.