Three people move into a 2BHK. Rent is ₹30,000. Splitting it three ways is easy - ₹10,000 each - right up until the third bedroom turns out to be a converted balcony half the size of the other two, and suddenly "equal" doesn't feel equal to the person who got it.
This is where most flat-sharing arrangements actually break down: not over big dramatic betrayals, but over a splitting method nobody agreed on out loud, which everyone is quietly unhappy with in a slightly different way.
Three ways people actually split rent
Equal split. Everyone pays the same amount regardless of room size, income, or how much they're home. Works well when the rooms are genuinely comparable and everyone's financial situation is roughly similar. Breaks down fast when it isn't.
Room-weighted split. You work out a fair ratio based on room size or which room has the attached bathroom, and split rent (not other bills) by that ratio instead of evenly. A common approach: get a rough rent estimate for each room individually (what would this room alone cost as a single-occupancy room nearby?), then split the total rent in that proportion. It takes one slightly awkward conversation to set up and then never comes up again.
Income-weighted split. Less common for flatmates who are peers, more common when one person earns significantly more - a working sibling and a student, for instance. Splitting proportional to income avoids one person being stretched thin while the other barely notices the rent leaving their account. This one needs the most trust, since it requires being honest about numbers with people you live with.
None of these is the "right" one. The failure mode isn't picking the wrong method - it's not picking any method at all and defaulting to "we'll figure it out," which quietly becomes "whoever remembers to ask first gets paid."
A worked example, so it's not abstract
Say total rent is ₹36,000 for three rooms. Room A has an attached bathroom and gets more light - a single-occupancy version of it nearby would rent for roughly ₹15,000. Room B is a standard room, roughly ₹12,000 solo. Room C is smaller, roughly ₹9,000 solo. That's ₹36,000 across the three estimates - conveniently the same as actual rent, though it won't always land that neatly.
The ratio is 15:12:9, which simplifies to 5:4:3. Split ₹36,000 in that ratio: Room A pays ₹15,000, Room B pays ₹12,000, Room C pays ₹9,000. In this case it happens to match the individual estimates exactly, because the estimates summed to the real rent - when they don't, you scale the ratio to the actual rent total instead of using the raw estimates.
The math takes five minutes once. The part that actually takes effort is agreeing on the room estimates honestly, which is exactly the "one slightly awkward conversation" mentioned above - and it really is just the one conversation, because once the ratio's set, it doesn't need revisiting unless someone changes rooms.
What happens when someone moves out mid-year
Splits set up for three people don't automatically work when a flatmate leaves and a new one moves in three weeks later - especially if the new person negotiated a different arrangement, or if the room ratio assumptions no longer hold with a different mix of people. The mistake most flats make here is assuming the old split just carries over by default, and then being surprised when the new person feels it's unfair without ever having agreed to it.
Treat a flatmate change as a legitimate reason to redo the split conversation, not an inconvenience to skip past. It's the same five-minute conversation as the first time, and skipping it just relocates the disagreement to three months later, when it's harder to have calmly.
Bills are a different problem than rent
Rent is one number, once a month, easy to reason about. Bills are messier: electricity varies with who ran the AC all summer, groceries get bought by whoever happened to be at the store, and the internet bill is the one thing that's actually genuinely equal since everyone uses it the same amount regardless of habits.
The practical fix is to not force bills into the same split logic as rent. A common working setup: rent splits by whatever method you picked above, but groceries and other variable costs get logged individually as they happen and split equally at the end of the month - because trying to weight "who cooked more" is a fight nobody wins, and it's genuinely close enough to equal most months anyway.
Electricity is the one exception worth handling separately if someone runs an AC unit in their own room that others don't use - that person can reasonably cover a larger share of just that bill, split by usage instead of headcount.
Agree on it once, in writing, before month one
The actual fix for most flat-splitting arguments isn't a better formula - it's having any formula at all, decided before the first rent is due, not renegotiated every time someone feels shortchanged. Write it down somewhere all three of you can see: "Rent splits 40/30/30 by room, bills split equal, groceries logged and split equal at month end."
That's the entire fix. Once it's decided and visible, there's nothing left to argue about except the numbers themselves - and numbers, unlike feelings, are easy to check.
This is exactly what a shared budget in BudgPay is for: set it up once with your split logic, log expenses as they happen, and everyone can see the same running total instead of trusting memory or a WhatsApp thread that's scrolled past.