Any tips for working out starting chain length for yolk of cardigan

Hi all, I’m looking at making a cardigan for my daughter without a pattern, just going to try and wing it. But I’m struggling to work out how to determine what my starting chain should be. I’ve made cardigans before so know how to do the increases in the four corners and at the front for a V neck style. But wasn’t sure if there was a formula people might use for working out how long my chain should be to begin with. E.g across the back between the increases, then adding the chain for each ‘shoulder’ part then adding the chains for the front two parts. I hope this makes sense. Any help or insights appreciated!