To tip or not to tip? That’s often the question for travelers. The answer varies depending on whether you are here at home or traveling abroad.

In a handful of countries such as Japan, travelers risk insulting waiters or hotel workers by offering a tip. But in other countries, such as the U.S. and Canada, not offering a tip can be insulting, says Kristen Bonner, a researcher for financial website GoBankingRates.

You should also know that while tipping is customary in some countries, like the U.S., it isn't customary in others. Those countries include Japan, South Korea, New Zealand, Brazil, and China, according to Bonner.

One way to make sure you know whether or not to tip is by turning to apps that can provide guidance in a pinch. Several tipping guides that will tell you how much tip is customary are available for smartphones. Among them are Global Tipping and Tip Like a Local for iOS devices and Tipping Bird for Android devices.

Another good idea is to make sure that you have cash on you. Before heading out on your travels, visit your bank to exchange big bills for smaller denominations. If traveling in the U.S., carry plenty of $5 or $1 bills, says Bonner. If you’re traveling outside of your home country, visit a currency exchange kiosk or bank to get local currency in small denominations.

Tipping Rules of Thumb

Keep these suggestions in mind while traveling.

Airports: In countries where tipping is the norm, such as the U.S. and Canada, tip porters who are checking in your bags at the curbside with $5 for one bag and an extra $3 to $5 for each additional bag.

Taxis: In the U.S. and Canada, tip your taxi driver 10 to 20 percent of the bill. The tip for a town car and limo driver is a little higher—15 percent to 20 percent. In Europe, the practice is to round up on a fare. So if your fare was €23, round up to €25. When in doubt while traveling in other countries, Bonner says rounding up is a good rule of thumb.

Restaurants: In the U.S. and Canada, it’s typical to tip 15 to 20 percent, or up to 25 percent if the service was excellent. For parties of eight or more, the tip may already be included. While some restaurants are beginning to do away with tips altogether, the practice isn't that common yet. In Europe, adding a tip of 5 to 10 percent is appreciated, but restaurants in some countries such as Italy already add a “service charge,” to your bill so you don't need to give an additional tip. You don’t need to tip in countries where tipping is not customary, such as in Japan and South Korea.

Hotels: At five-star hotels in the U.S. and Canada, tip a bellman $5 per bag. At less highly rated hotels, a tip of $1 to $2 per bag is customary. Many travelers forget to tip the housekeepers before checking out, Bonner says. She recommends that you tip $2 to $10 for each night of your stay. You can tip doormen between $2 to $5 per day. If the concierge has been helpful with things like making reservations, you can tip them anywhere from $5 to $20. In Europe, hotel staff expect to be tipped. The practice varies considerably in regions such as Asia and South America.