It was in 2010, the year I turned 26, that I organized the last group dinner used to celebrate my birthday. I love eating out at restaurants—so much so that I made a career out of doing it—but it was at that time I realized how stressful it could be as one of the guests, watching anxiously as fellow diners ordered drink after drink or opted for the Steak For Two for one. Namely, knowing that at the end of the meal, there was inevitably going to be a tense 20 minute conversation-turned-argument, turned-strong-arming-turned-resignation—and some, if not all except for the birthday girl—could leave the table disgruntled.
In short, group dining is the worst. Even if it's a smaller group and close-knit, there's an inherent awkwardness to staring down at the bill together. If you're a teetotaler who just ate the side salad at a steakhouse, you may feel you shouldn't have to carry those who ordered wine and the evening's special. Then there are those "heroes" who feel compelled to break down the tab item-by-item, person-by-person, involving advanced mathematical equations to determine to the penny what each diner owes. If you need to employ more than two mathematical operations, it's a goddamn waste of time.
In short: everyone should just split the bill evenly.
Yes, even if you didn't drink. Yes, even if you are allergic to avocado and the table ordered pricey bowls of $26 guacamole. It's the easiest thing to do and the right thing to do.
Look, there are going to be times when you're ponying up an extra $10-20 than you would had the split been person-by-person, but there are also going to be times you're getting off easy in terms of a financial burden. That's the karmic cycle of group dining: sometimes you win and sometimes you're funding your friends' appetites.
But the scales tip enough over one's lifetime that being intractable over one lousy dinner is enough to give you a bad reputation, or worse, spoil the evening for everyone who'll then be forced to pay more per individual since you stood firm on the $12.15 for the salad plus another $15 to cover the cost of the birthday person, if applicable. And then how do you even figure in your percentage of tax and tip? Nightmare.
Quick shout out to the person who throws down some cash and leaves early. GFY!
The most important rule when it comes to this even-split method is communication. If everyone knows at the top of the meal that the bill is going to be evenly divided, nobody can fire back with any shenanigans when the check arrives. It'll make the meal more relaxing, too, as everyone can order as they'd like and not worry too much about being deemed too flashy (though if you're ordering a $100 entree when everyone else is around $30, perhaps best to check yourself there).
Your wallet isn't the only concern with elaborate bill-splitting techniques. As a longtime waitress, I can confirm that receiving an annotated bill with names, amounts and a stack of credit cards is about the worst thing you can do (double that if you're a shitty tipper). Some restaurants won't even let you split the bill with more than a few credit cards, which brings me to my next point...
Yes, cash is antiquated and maybe we won't even be using it a decade from now but it's still the easiest, most efficient way to split a dinner among a group. It's a very satisfying experience to hand a few $20 bills down the table and be done with it. Not to mention tipping servers in cash is always preferable to credit, where they're subject to taxes and waiting on the weekly checks instead of walking out the door with their money up front.
If you don't have the money to spend on a group outing—and we've all been there—you should feel completely confident saying you can't make the dinner but you'll meet up for drinks. Anyone organizing a restaurant meal should be cognizant of other people's budgets and understand that it's not going to be a fit for everyone at all times. Missing out sucks, sure, but it sucks less than feeling financial instability when you're spending more money than you're able to.
And birthday/special event planners should be mindful, too. Pick a restaurant that's of a lower price point and therefore more welcoming to people of all budgets. Or pick a BYOB place so the booze—always the most expensive part of any meal—can be controlled by the individual diner.
Or just retire the restaurant group dinner altogether. Nobody cares about your birthday that much anyway.
UPDATE: Here's a rebuttal.