There are no U.S. tax credits per se for married vs. unmarried taxpayers. Depending on the relative incomes of two spouses, there can be a so-called "marriage penalty" or "marriage reward" from combining two incomes on a joint return, but that alone probably has very little impact on whether people choose to get or remain married.
In fact, a large chunk of existing tax law deals with all the possible combinations of households with children and parents, where the parents may or may not be living together, and may or may not be married to each other. It is designed to fairly accomodate unmarried people, not to encourage marriage.
The tax penalty (which is very real for many SV and NYC earners) is one reason I’ve decided to never get married. The other being that the insane one-size fits all contractual aspects of marriage that cannot be changed.
A vengeful judge and spouse can easily wreck one’s finances unfairly.
In fact, a large chunk of existing tax law deals with all the possible combinations of households with children and parents, where the parents may or may not be living together, and may or may not be married to each other. It is designed to fairly accomodate unmarried people, not to encourage marriage.