Equal, exact, or percentage: choosing how to split

Three buttons: equally, by amounts, by percentage. Most people press the first one for everything, which works until the evening someone orders a starter and someone else orders four cocktails. Here's when each method is the fair one, and what the app does with the paise.

Equally: the default, and usually correct

A ₹2,400 dinner between four people is ₹600 each. Nothing to think about. The interesting case is when the total doesn't divide cleanly:

Money is counted in whole paise, so a third of ₹100 doesn't exist. Someone has to take the extra paisa, and the honest rule is to give it to whoever's exact share had the largest fraction left over. Over a year of dinners it's worth nothing. Over a year of dinners it also never once fails to reconcile, which is worth quite a lot.

By exact amounts: when a rupee figure belongs to one person

A ₹2,480 grocery run where ₹680 of it is Sam's protein powder. The rest is genuinely shared:

Exact amounts are also what you use for a restaurant bill where everyone ordered differently. Work out each person's share of the subtotal, scale it for tax and tip, and type in four numbers. The app won't let you save until they sum to the total, which is the check you'd otherwise skip.

By percentage: when the ratio is the agreement

Rent split by room size. Bills split by who's actually home. A couple who count as two people in a four-person flat. In all of these, the ratio is the thing you agreed on, and the rupee amount changes every month:

Percentages have to total exactly 100%. Ninety-nine point nine isn't a rounding difference, it's an unfinished decision, and the app says so rather than silently absorbing it.

Choosing, in one line each

• Did everyone consume roughly the same amount? → Equally, unticking anyone who wasn't in it.
• Can you point at a rupee amount that belongs to one person? → Exact amounts.
• Is there a standing agreement about the ratio? → Percentage.

Five mistakes that make friends quietly annoyed

1. Splitting equally with someone who wasn't there. The most common one, and the one people never mention out loud.
2. Rounding to a nice number. "Just make it ₹1,100" on a ₹1,127 share is ₹27. Thirty times a year it's ₹810 that came out of one specific pocket.
3. Skipping small ones. Small and frequent is the expensive kind. The ₹90 auto three times a week is ₹14,000 a year.
4. Changing the method retroactively. Re-splitting last month's expenses because someone raised it is how a group stops trusting the ledger. Fix genuine errors; leave settled history alone.
5. Writing "stuff" in the description. Nobody disputes an amount they can recognise. Everyone disputes "stuff".

Percentages and amounts do different jobs

Percentages express a ratio; amounts express an outcome. When you know the ratio and the total moves, use percentages. When you know the answer in rupees, use amounts. Trying to express "Sam owes exactly ₹680 extra" as a percentage is a calculation you'll get subtly wrong, every month, in a way nobody notices for half a year.