other possible solutions - note there is no precise method
1) he should pay estimated taxes for his share of the taxes
2) before filling calculate each one's share of the taxes and then have him reimburse you for his share.
he pays 100% of the self-employment taxes and then the regular income taxes are split in proportion to each one's share of taxable income. if you itemize deductions this will require a consensus on how to split them
3) prepare two single returns or married filing separate returns then calculate his taxes by dividing his taxes by the total of the taxes on both returns multiplied by the tax liability on your joint return. a joint return is filed. you might need the desktop software to do this because there can be only one return in an online account. there may be issues in trying to prepare single or MFS returns because some items may be limited.
unless both of you are separating your assets, the family will be in the same position regardless of how the taxes are split except there will be less in total if married filing separate
