What are the real tax trade-offs of getting married, the so-called marriage penalty or bonus?

Marriage can help or hurt depending on how similar your incomes are. A 'marriage bonus' typically occurs when one spouse earns much more than the other, because combining incomes on a joint return can pull the higher earner's dollars into lower brackets than if taxed alone. A 'marriage penalty' can hit two high, roughly equal earners whose combined income pushes them into a higher bracket or past phase-outs faster than two singles would. Most brackets are set at double the single amounts to reduce penalties, but some thresholds are not, and certain credits phase out at levels that do not double. The IRS bracket tables let you model both scenarios before you decide how to file.