Write it down in the room, on the day, before anybody leaves. That is the whole answer and it costs nothing but ten minutes of mild awkwardness. Every horror story in songwriting starts with three people agreeing they would sort it out later, and later arriving five years on when the song is in an advert and one of them has stopped returning calls.
The default that actually works
Split it equally between everyone who was in the room contributing. Three writers, a third each. Four writers, a quarter each.
This is what most professional writing rooms do, and they do not do it because it is precisely accurate. They do it because it is the only arrangement that can be agreed in thirty seconds, cannot be re-litigated later, and does not put a price on anybody's afternoon. Equal splits are a social technology, not an accounting one.
If somebody genuinely was not writing — they sat in, made coffee, offered encouragement — they are not a writer and this is the moment to say so kindly. Adding a non-writer to be nice is how splits become meaningless.
Why 'I wrote more of it' cannot be settled
Because there is no unit of songwriting. Is the melody worth more than the lyric? Is the chord progression worth more than the line that made the chorus land? Is the person who wrote eight words that changed everything worth less than the person who wrote forty that did not?
Nobody has ever answered these questions to everybody's satisfaction, and the attempt has ended more collaborations than bad songs have. An argument with no possible resolution is an argument you should decline to start. Equal splits decline it.
Unequal splits are fine when everyone proposes them and everyone agrees without pressure — someone who arrived with a finished verse and chorus asking for a larger share is not being unreasonable. The rule is that it happens before the song is finished, not after somebody wants to use it.
The distinction that causes the most trouble
The song and the recording are two different pieces of property, with two different sets of owners.
Songwriting splits cover the composition — the melody and the words. That is what a split sheet records, and it is what your PRO and the MLC pay out on.
The recording is separate. A producer who did not write anything may still be owed a share of the master, or a fee, or points. A session player might be owed a fee and nothing else. None of that belongs on the split sheet and none of it changes the songwriting percentages.
Conflating the two is behind a large share of the disputes that end up with lawyers. Settle them separately and say out loud which one you are settling.
What the sheet has to contain
Nothing exotic. A usable split sheet records:
The song title and the date it was written. Every writer's full legal name — not the artist name. Each writer's PRO and their IPI or CAE number, which is how the societies identify a human being. Each writer's publisher, or 'self' if there is not one. Each writer's percentage. And a signature from every one of them.
The percentages must total exactly 100. A sheet that adds up to 99 or 105 will be rejected downstream and will have to be chased, usually at the worst moment.
Contact details help. Five years later, an email address on a piece of paper is sometimes the only way anyone finds anyone.
Where it goes afterwards
A signed split sheet in a drawer does nothing by itself. It is the source document for three registrations, and the registrations are what move money.
The splits go into your PRO registration for the song, into the metadata your distributor delivers with the release, and into the MLC so that mechanical royalties are matched to the right writers. Mismatched splits across those three is a standard reason for royalties to sit unpaid and unmatched.
Do it while the sheet is in front of you. It is the same information typed three times, and it takes less time than explaining later why the money went to the wrong person.
None of this is legal advice. A split sheet is a record of what people agreed, and for anything substantial a real agreement drafted by a lawyer is the grown-up version.
Ten minutes of mild awkwardness in the room, or years of it afterwards. Those are the two options and there is no third.
Three pages on this site that carry it further: the split sheet to fill in and print, getting the credits recorded properly, and the songwriting side of the room.
Fill One In Right Now
There is a split sheet on this site that you fill in on screen and print, with the percentage total checked as you type. It works on a phone, which is where most of these conversations happen.