Split any trip, rent or dinner bill fairly, in one prompt (the SPLIT setup)

This is the setup from the reel. Every trip with friends ends the same way: one person left early, one person paid for the room, and the group chat has three different answers for who owes what. This prompt makes the split fair and shows the math, so nobody has to argue about it.

Since the GPT-6 update in October, the ChatGPT app can draw the split as a little tool right inside the chat, with numbers you can change. If you only get text back, the numbers are the same; ask it once more to "make it a bill splitter I can change".

What you need

• The free ChatGPT app on your phone. Claude and Gemini can do the split too.
• The total you spent, and who was there for how long.

The prompt

Tap copy on the box below, change the things in square brackets, send.

Help me split a shared bill fairly.

What we spent: [total amount] rupees in total for [the trip / the flat this month / the dinner].
Who was there: [names, and how long each one stayed or what each one joined for].

1. Before you split anything, ask me which costs were shared by everyone no matter how long they stayed (like the train tickets) and which costs depend on nights stayed (like the room). Wait for my answer.
2. Then make me a bill splitter I can change: each person, what they owe, and a line I can paste into the group chat.
3. Show the math in one line per person so anyone in the group can check it.

Step 1 is the one that matters. Without it, the easy answer is to split the whole bill by nights, which makes the person who left early pay less for the train they still took.

What it gets wrong

It splits to the paisa. On my run it gave one person 5,114.28 and two people 5,114.29, to keep the total exact. Nobody pays paisa. Round everyone to the rupee and let whoever booked the room eat the few rupees.

It can't see who already paid. My prompt didn't say who paid for the room, so it said what each person owes in total, not who sends money to whom. Add one line, "Neha paid for the room and Arjun paid for the train", and ask it who should pay whom.

And it believes what you tell it. If you forget that someone skipped a dinner, the split is wrong and it looks right. Read the math lines before you send it to the group.

The measured run

This was a made-up trip, so you know what you're reading. 18,400 rupees, 4 people, three stayed 4 nights and one stayed 2. One run, timed, on 19 October 2026. Not on the phone app: I sent the exact prompt above through OpenAI's GPT-6 Luna (the model free ChatGPT uses) from the Codex command line on my desktop, so I got text back, not the little tool, and the time includes the tool starting up.

• First answer, in 11 seconds: it didn't split anything. It asked how much of the 18,400 was shared by everyone and how much depended on nights. That's step 1 doing its job
• My answer: train tickets 4,000, shared by everyone; the other 14,400 was the room
• Second answer, in 21 seconds: 1,000 each for the train, the room split across 14 person-nights (4 + 4 + 4 + 2) at about 1,028.57 a night
• The split: 5,114.28, 5,114.29 and 5,114.29 for the three who stayed all 4 nights, 3,057.14 for the one who stayed 2. Total 18,400.00. I checked the math by hand; it's right
• Wrong: the paisa, and no "who pays whom", the two catches above

By hand: not timed. I'm not going to guess a number for you. Next trip, time the group chat argument once, then time this.

Where the longer version lives

The Rabbit Hole is the community where I post the setups, the ones that worked and the ones that didn't. Ask there and I answer in the open, so the next person with your question finds it. It's free to join; Premium ($5 a month) adds weekly office hours. skool.com/the-rabbit-hole-3206