IMHO if your product and company works, you're in it for a long time. That means your co-founder should keep their motivation long-term as well.
If your first sale happens within the next few months, I would keep a 50/50 split just because they will put in a lot of effort in the future. Alternatively, you could start your vesting now and and the other founder could start vesting as soon as he joins full-time. Not sure if this is legally possible.
Another option would be to count the difference in time you spent on it and translate that into equity and ask your co-founder to give you that (like 45% vs 55% equity split). I wouldn't go more than 5%, since I prefer to keep things even. Again, you've got a long road ahead of you, so make sure both of you feel comfortable with the split and with future obligations as well.
If your first sale happens within the next few months, I would keep a 50/50 split just because they will put in a lot of effort in the future. Alternatively, you could start your vesting now and and the other founder could start vesting as soon as he joins full-time. Not sure if this is legally possible.
Another option would be to count the difference in time you spent on it and translate that into equity and ask your co-founder to give you that (like 45% vs 55% equity split). I wouldn't go more than 5%, since I prefer to keep things even. Again, you've got a long road ahead of you, so make sure both of you feel comfortable with the split and with future obligations as well.