Married filing separate for the first time

Why do you think you have to file MFS because your spouse began a business?    Is he a sole proprietor?    That is not a reason to file MFS.   His self-employment income can go on your joint return.  Before you go forward.....please provide some details.

And...if you really are set on filing married filing separately, you need two accounts.   Start a new account for each spouse with a new user ID.   It is too difficult to remove the embedded spouse information from an account that was used for joint returns in the past.

If you were 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 disadvantages of filing separately include: 

You cannot get earned income credit, 

You cannot get education credits or deductions for student loan interest. 

You cannot get the childcare credit

You have a lower amount of income on which to base the refundable additional child tax credit

85% of your Social Security benefits will be taxable even with no other income 

The amount you can contribute to a retirement account will be limited.

Capital loss deduction is less than if you file jointly

You cannot get the $6000 senior deduction

You cannot get the deductions for overtime or tips

 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) and your returns become very complicated.

 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

https://ttlc.intuit.com/turbotax-support/en-us/help-article/taxation/married-filing-separately-community-property/L11CeLUMs_US_en_US?uid=m69ousyh

Was he the primary on the account?  If so, then you would need to create a new account.  You will still need to include his name and SSN on your return, but list your name first and then when asked say you want to file a separate return.  

Also, having a business does not require you to file separate returns unless this is due to tax planning such as you don't want to be responsible for his self employment taxes.  However, if it is because he is filing a schedule C with the return, this can still be done as a joint return. 

Married Filing Jointly vs Separately: How Should You and Your Spouse File Taxes?