Its called tax bracketology. If you are married, you have 2 filing options, married filing jointly or married filing separately. When you are married filing jointly and both spouses have income, the combining of incomes pushes you up the tax bracket. Like piling income on income. Think of it like one ladder instead of 2 ladders. If you were single, you both would get the advantage of the lower rungs in the ladder. But if you are climbing that 1 ladder together, only 1 will get the advantage of the lower rungs and the other will have to start at a higher rung when you run out of gas. That's kind of what the tax brackets are like. When you were single, you both got to take advantage of the lower rates as your income climbed up the single rate schedule. But when you are married, there is only one rate schedule so for your combined income, only one of you will get the advantage of the lower rates then other persons income will be taxed toward the higher portion of the bracket.
You can try figuring it married separately and it might help by probably not. Here is a link to the IRS W-4 app that will help you with your withholding for 2021.
Are you trying as Single or Married filing Separate? If you are Married Joint should be better than MFS. So you could be doing it wrong.
Unless you have a specific reason to file separate returns,
It is usually better to file Joint. Joint has the lowest tax rates and the highest Standard Deduction. And if you are in a Community Property state MFS gets tricky to figure out. Here's some things to consider about filing separately……
In the first place you each have to file a separate return, so that's two returns. And if you are using the Online version that means using 2 accounts and paying the fees twice.
Many people think they come out better when filing Married Filing Separate but they are probably doing it wrong. If one person itemizes deductions then the other one must itemize too, even if it's less than the standard deduction, even if it is ZERO!
And there are several credits you can't take when filing separately, like the
EITC Earned Income Tax Credit
Child Care Credit
Educational Deductions and Credits
And contributions to IRA and ROTH IRA are limited when you file MFS.
Also if you file Married Filing Separately up to 85`% of your Social Security becomes taxable right away even with zero other income.
To compare Joint to MFS. If you are using the Online version, do NOT change anything on your return. You would have to start with a new account and do a test return. You don't have to pay unless you want to print it out. So you might need 3 accounts, one for Joint and two MFS, one for each spouse.
How to Compare Joint to Married Filing Separately
How to start another return in the Online version
It would be better to use the Desktop CD/Download program. It can do unlimited returns and has a What If worksheet to compare them and many other advantages over the online version.
You can buy the Desktop CD/Download program here