The conversation is the hard part, not the arithmetic
Most money problems between two people are not arithmetic problems. The numbers are usually knowable in an afternoon. What is hard is saying the thing out loud without it landing as a criticism, and hearing it without treating it as one.
That is why these conversations tend to arrive sideways β as irritation about a specific purchase, or a comment about something else entirely, weeks after the actual worry started. The purchase is rarely the subject. It is just the thing that was concrete enough to mention.
The posts here are about the mechanics of the conversation itself: how to open it, when to have it so it is not a crisis, and how to handle the case where you want different things and neither of you is wrong.
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Or see it on your own numbers
Pairly holds the rent, the bills and the subscriptions for two people, splits them the way you agreed, and shows the same picture to both of you. No bank connection, no card to start.