Nobody wants to be a jerk when confronted with a check or tip jar. But it's hard to talk about cash, and it can be even harder to calculate how much to tip when closing out a bar or restaurant tab. Plus, tipping etiquette is constantly evolving, which makes the process a tad more stressful than it needs to be.

So, let's make it easy.

We've enlisted an anonymous restaurant server, Emily (surname and workplace withheld), to share her two cents about leaving dollars and cents. She’s slung plates and collected tips in Los Angeles, Hawaii, Phoenix, and Chicago, amassing a multi-city body of knowledge on the subject. With Emily's help, and with no holds barred, we'll visit this complicated, hush-hush intersection of money, morality, and math.

How much to tip at the bar?

If you're closing out a tab on a card, leave 20%. If you're using cash to pay as you go, do what Emily does and slap down singles. "I tip a dollar a drink on simple things," she says, referring to items such as beer and shots. However, she says:

"I tip 20% on craft cocktails," even when using cash.

That's because she's paying for the bartender's time. In the three minutes it takes to grate rare snozzberry zest over an artisanal negroni, the bartender could have netted a dollar each on six simpler drinks. Paying for time also means that a gold-star patron will tip a dollar on a free glass of water.

What about the coffee shop?

Tipping at coffee shops is similar, but not identical, to tipping at bars. Even Emily sometimes skips the tip at a café. "But never at a restaurant or bar," she adds quickly. "I would die." Baristas understand that they won’t receive tips from everyone. Just as with bars, however, you want to respect their time. If you look down at your cappuccino foam to find a painstaking replica of a Hieronymus Bosch triptych, then go ahead and tip more than one lonely Washington.

What if there's a tip jar?

It's always nice to help fill up a tip jar, especially if you appreciate the employee's help or craftsmanship. It's not as crucial as tipping on a bill or tab, but you can’t go wrong with generosity—especially if you’re a regular at the establishment in question. When it comes to tip jars, don't worry about percentages or dumping in a few coins. Emily says servers don’t mind change:

"Change adds up! It's fine.”

She then issues a swift, salty addendum, which we'll sanitize here so you can send this article to your mom: "I mean, but still, eff your pennies."                                

What if I'm at a restaurant?

Simply put, always tip at least 20%. Then double-check your math and confirm the 20%. That’s because you're actually paying your server's wage at a restaurant. "If they under-tip," Emily explains, "the server is still taxed on [the expected total], and also needs to tip out other parts of the house based on sales." In a cruel twist of algebra, Emily says this sometimes means that "the server pays to serve that table."

So, what if I'm at a restaurant with a Groupon?

Again, you're tipping for time and service, not ingredients. So if you have a Groupon, tip 20% of the full, pre-Groupon value of the bill. Think about it: with or without a Groupon, your server is still balancing the same heavy plates, fielding the same questions about substitutions, and knitting the same napkins by hand. Of course, 20% is just a rule of thumb. If the service is particularly good, tip 25% or more. If it's dreadful, take it up with the manager.

What if I'm with a large group?

"If you are a large group," says Emily, "it's often that you are the majority of the server's [financial] intake for the night, so just be respectful."

Servers’ biggest group-related grievance? Check-splitting.

The primary reason servers hate split checks has to do with—and here’s that word again—time. First, the server tracks down the order of every individual in the gaggle. This is an especially time-consuming feat at the end of the night, when food comas and multiple rounds of drinks muddy diners' memories. Then, it’s time to re-enter the whole meal into the restaurant’s system.

According to Emily, there's a second reason servers hate to split checks, though, and it's even more serious: "When tables split checks, often the tip gets screwed up. A lot of times, the last person is supposed to tip on the total bill but only tips on their amount, screwing the server over."

If you absolutely must split the check, then let your server know ahead of time, double-check your calculations, and communicate with your tablemates. If you follow these simple guidelines on how much to tip, both your server and your dining party can leave the restaurant without any regrets.

More stories to brush up on your table manners:

Who Should Pick Up the Check on the First Date

The Right Way to Split a Group Check