Filing Married Filing Separately (MFS) instead of Married Filing Jointly (MFJ) often leads to reduced access to credits and deductions. Many credits (like certain education credits, earned-income–type credits, and some child-related credits) are limited or disallowed for separate filers. Also, certain deductions and tax benefits phase out more quickly for MFS filers, and some tax credits are unavailable entirely. The practical consequence is that couples who file separately may face a higher combined tax bill than they would if they filed jointly. MFS is sometimes chosen for specific reasons — separation of liability (if one spouse has questionable tax issues), privacy, or to keep separate accounting — but it is usually not the default choice purely to save tax. Before electing MFS, consider the likely loss of tax benefits and run the numbers both ways.

There are scenarios where MFS is sensible: when one spouse has significant, separate issues (large medical deductions tied to one spouse’s income that benefit from separate AGI calculations), or when spouses want to avoid joint liability for tax under certain legal circumstances. But because many credits and deductions are constrained for separate filers, couples often find that MFJ yields lower total tax. If a couple considers MFS, they should model both filing statuses with realistic numbers, including lost credits and altered deduction phase-outs. Additionally, communication with a tax professional is wise when legal liability, student loan repayment plans, or state tax differences interact with the federal filing choice — these factors can change the best practical decision.