Best Wishes!
It is not easy to compare MFJ to MFS using online TT but you can do it. Since you only get one return for each account and user ID, you have to use 3 accounts and user ID’s—one for MFJ and two for each of the MFS returns. Compare, choose, and file—and pay—accordingly.
It is much easier to do this comparison using the desktop version of TT installed from a CD or downloaded to your own computer. You pay once for the software and you can prepare multiple returns easily, and it has a “what if” feature that allows comparisons.
WHAT IF…?
If you are using Desktop software:
If you were legally married at the end of 2024 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 $29,200 (+ $1550 for each spouse 65 or older) for 2024. 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.
How to start a new joint return
You will not be able to merge two previous TT account to start your new joint return. You can transfer ONE of your 2023 returns into a new return, so choose the most complicated one. The other spouse’s information needs to be entered manually. The first name you enter will be the “primary” taxpayer——and in subsequent years you need to keep the names in that order—do not try to change the order of the names.
When you enter the primary spouse’s information in My Info, you have to answer the question "Were you married?" If you click the button for Married, then a drop down will appear that asks, "Do you want to file this return together with your spouse?" Then you choose YES to file a joint return. You enter your spouse's information into My Info. Whenever you are entering income information there should then be a spot for you and for your spouse's income information. WATCH for the names as you enter income on the screens. Or when you click to add income it will prompt you to choose which spouse had the income.
When you prepare a joint return you include all the information for both spouses on the SAME tax return. Include all of your personal information, all of your income from every source, all dependents (if any), all credits and deductions for both of you. You get ONE refund with both names on it.
HOW TO START A NEW RETURN TO FILE MARRIED FILING SEPARATELY
When you enter your own information in My Info, you have to answer the question "Were you married?" If you click the button for Married, then a drop down will appear that asks, "Do you want to file this return together with your spouse?” Your answer needs to be NO. Then it will ask for information about your spouse—-their name and SSN which you must enter. EACH spouse has to file their own separate return. And you have to follow all of the rules which include that if one of you enters itemized deductions, the other one must also itemize. Or…you both use standard deduction. If you are in a community property state there are additional rules and more information to enter.
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
How can I compare Married Filing Jointly with Married Filing Separately? Works with TurboTax Desktop
What does getting married mean for my taxes?
More information - MFJ vs MFS
TaxCaster - estimate your refunds
Look at those huge answers for a simple question with a simple answer.
If using Turbotax online, you need 3 accounts with different user names and passwords (they can be linked to the same email) -- one joint and one for each separate spouse return. You don't pay for these accounts until you file, but if you decide to file separately, you have to pay for each return separately unless you qualify for free filing.
If using Turbotax installed on your own mac or PC (the desktop version, from a download) you can prepare 3 returns without paying extra, or you can prepare 1 joint return and then look for the "what if..." worksheet.
The key thing to remember is that when filing separately, both spouses must use the standard deduction or both spouses must itemize, even if there are not enough deductions to spread around. It is not allowed to load all the deductions on one spouse and the other spouse claim standard.
Most of the time, joint filing is better, but rarely it is not, the only way to know for sure is to test it.