Your current split is fixed. This means that in order to change it you have to do exactly what you're doing: a painful, confusing renegotiation. This will result in another fixed split which will lead to another painful, confusing renegotiation. This will continue throughout the formation of the company. Each time putting you a odds with your partner.
Your split is little more than a guessing game. The advice you are getting is just more ways to guess. When you do a fixed equity split the guess is always wrong.
Time-based vesting is simply a band aid on a bad split decision.
You need to change your approach. The good news is that there is a way to guarantee
you get a perfect split no matter what happens. It is a self-adjusting model called Slicing Pie
and it's based on a simple principle: a person's % share of the equity should always equal that person's % share of the risk.
For example, pretend you and your partner are playing Blackjack. You agree to a 50/50 split on the winnings and each bet $1 on the same hand. If you win, you will each get half.
Now, say the dealer deals two aces. This wasn't what you were expecting, but you want to take advantage of the opportunity. You split the aces and double-down. Your partner is broke, so you put down $2 more. Now your total bet is $3 and his is $1. The 50/50 split doesn't look fair anymore, even though you agreed to it. It should be clear that you deserve more. Specifically, you should get 75% and he should get 25%. Your share of the winnings should reflect your share of the risk.
Slicing Pie works the same way.
When you invest in a startup you are essentially placing a bet on the future outcome of the startup. The value of your bet is equal to the fair market value
of the contributions you make.
Using a function of these "bets", the Slicing Pie formula allocates equity based on your risk relative to others. It not only allows you to calculate a perfect split, but also tells you the right buyout price when someone leaves.
It is the worlds only way to create a perfect split. Everything else will cause problems.
I've written a retrofit guide
that will help you figure out what the right split should be based on the Slicing Pie model. Then, you continue to use the model until you reach break even or Series A investment.
You will LOVE it!