First----as to whether to file jointly or separately:
If you are legally married at the end of 2025 your filing choices are married filing jointly or married filing separately when you prepare your 2025 return.
Married Filing Jointly is usually better, even if one spouse had little or no income. When you file a joint return, you and your spouse will get the married filing jointly standard deduction of $31,500 (+ $1600 for each spouse 65 or older) for 2025. You are eligible for more credits including education credits, earned income credit, child and dependent care credit, and a larger income limit to receive the child tax credit.
If you choose to file married filing separately, both spouses have to file the same way—either you both itemize or you both use standard deduction. Your tax rate will be higher than on a joint return.
Some of the special rules for filing separately include: you cannot get earned income credit, education credits, adoption credits, or deductions for student loan interest. A higher percent of your Social Security benefits may be taxable. In many cases you will not be able to take the child and dependent care credit. The amount you can contribute to a retirement account will be affected. If you live in a community property state, you will be required to provide additional information regarding your spouse’s income. ( Community property states: AZ, CA, ID, LA, NV, NM, TX, WA, WI)
If you are using online TurboTax to prepare your returns, you will need to prepare two separate returns and pay twice since with online, you get one return per fee.
https://turbotax.intuit.com/tax-tips/marriage/should-you-and-your-spouse-file-taxes-jointly-or-separately/L7gyjnqyM?srsltid=AfmBOopGqCNexowW0pYgvsf7ycIkrx4VjO_63UXv6vSnfu3UEGQiKQTh
https://ttlc.intuit.com/turbotax-support/en-us/help-article/income/getting-married-mean-taxes/L2RgmagpE_US_en_US?uid=m69on7t0
You do not change your name with the IRS. You change your name with Social Security, and make sure that when you prepare your 2025 tax return that you use the name that matches your most current Social Security card.
What you put on your W-4 with your employer does not go to the IRS--it only goes to your employer to let the employer know how much tax to withhold from your paychecks. The information on your W-4 does not dictate how you have to file your tax return. If you want to have your tax withheld as if you are single you can do that and still file your tax return as married.
https://turbotax.intuit.com/tax-tools/calculators/w4/
https://www.irs.gov/individuals/tax-withholding-estimator
https://www.irs.gov/pub/irs-pdf/fw4.pdf
