My husband and I are now separated so will file married but filing separately. We filed joint since being married. Do I need his information still?

[xmasbaby0]

Yes. 

If I am filing a separate return why do I have to list my spouse’s information on my return?

Even if you file separate returns (the worst way to file) you each have to list each other's SSN's and some other information on your own tax return.  The IRS can then cross check to make sure you are not "double dipping" for itemized deductions, dependents, etc.

If you are in a community property state, there is more information that will be needed.

Community property states:  AZ, CA, ID, LA, NV, NM, TX, WA, WI

https://ttlc.intuit.com/questions/1901162-married-filing-separately-in-community-property-states

https://turbotax.intuit.com/tax-tips/marriage/five-tax-tips-for-community-property-states/L4jG7cq7Z

[AmyC]

Maybe. You can file MFJ or MFS and maybe HOH when you are still married. Both names and numbers go on the MFS tax return so the IRS can cross check. If one of you itemizes, you are both required to itemize. There are many lost credits when filing separately. I recommend you go through a quick quiz to determine what you can and should file. See What Is My Filing Status?

Here is a great article by Turbo Tax on MFJ vs MFS and another on your options and qualifications, What is my tax filing status (single, married, etc.)?

[Mike9241]

while filing MFS usually costs more in combined taxes than MFJ what you need for MFS is his Social Security Number and also, both must determine whether to use the standard deduction or itemize.  MFS may result in the loss of some tax credits. 

I'll point out that if you lived apart from your spouse for the last 6 months of 2023 and you paid more than 1/2 the costs of maintaining a household for yourself and a qualifying child that lived with you for more than 6 months the proper filing status is Head of Household. you need no info from him for this filing status

[xmasbaby0]

If you were legally married at the end of 2023 your filing choices are married filing jointly or married filing separately.

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 $27,700 (+$1500 for each spouse 65 or older)  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. Your limit for SALT (state and local taxes and sales tax) will be only $5000 per spouse. 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://ttlc.intuit.com/questions/1894449-married-filing-jointly-vs-married-filing-separately

https://ttlc.intuit.com/questions/1901162-married-filing-separately-in-community-property-states

https://ttlc.intuit.com/questions/1894449-is-it-better-for-a-married-couple-to-file-jointly-or-separ...

Am I Head of Household?

https://ttlc.intuit.com/questions/1894553-do-i-qualify-for-head-of-household

https://ttlc.intuit.com/questions/2900097-what-is-a-qualifying-person-for-head-of-household

If you qualify as Head of Household, when you enter your marital status (single or married filing separately) into MyInfo, and then enter your qualifying dependent, TurboTax will offer HOH as your filing status.

[Opus 17]

Yes, but usually only his social security number.  If the family had a Marketplace health insurance plan and received a subsidy, you might need some income information.  

Note regarding filing status.  While it is true that filing jointly is allowed (if you agree) and often results in lower taxes, what the others did not mention is that when you sign a joint return, both spouses are equally and jointly liable for all income and claims, and if there is an error, deficiency, or omission, the IRS can come after either spouse, or both, or whoever has the most money to seize, even if it is not that person's fault.  Filing separately may be the better option when you are in the process of separating and divorcing.