List of caveats I can think of:

* Covers regular federal income tax only. Does not cover any of the taxes on Schedule 2, nor any state/local taxes.

* Assumes both individuals take the federal standard deduction as Single (not Head of Household).

* Assumes no other credits or deductions.

As a result, this can potentially understate marriage penalties for dual-income couples with kids.

https://taxpolicycenter.org/briefing-book/what-are-marriage-...