What is the alternative marriage calculation for the Premium Tax Credit?

If you need to repay some of the advanced payment of the premium tax credit that you received then the alternative marriage calculation may lower the amount you must repay. It allocates 50% of your household income to each spouse and calculates the allowable credit for your pre-marriage months off of that amount.

The alternative calculation can only reduce the amount you have to repay and can't result in an additional credit.