Filing married separately – do I divide every individual box value by 2?

[reticulating]

If I want to file married separately, do each of us take the value of every box for joint accounts (banks, brokerages) and divide by 2? This would mean that if we sold a stock in a joint brokerage account, values like "sale proceeds" or "cost basis" are each divided by 2. The same goes with individual fields in 1099-INT and 1099-DIV forms. Is this the right way to do it, or does TurboTax automatically handle the split?

If relevant, we're based in California.

[DMarkM1]

It depends.  CA is a community property state. That means income items such as wages and interest and dividends and stock sales are typically considered community property.  Generally, to figure each spouse's income you must add 50% of all community property with 100% of each person's individual property (income).  TurboTax does not automatically handle the split as only the taxpayers know who owns the income (property).  

Wages are community property and so all wages are totaled and then split 50/50.  Property/income such as interest, dividends and stock sales, etc could be either community or individual.  If the accounts were owned and/or stocks purchased by the individual prior to marriage then the income belongs to that individual only.  If the accounts were opened/stocks purchased after marriage then they are community and like wages are added together and split 50/50.  

In TurboTax for each taxpayer after entering the income items on the return according to the social security number that the income has been reported under on the form (W2s, 1099s) and then, if itemizing, entering each persons share of deductions (by agreement; could be 50/50 or something else), then a community property income adjustment is made on each return.  One return gets a positive and one a corresponding negative.  

Note: if one spouse is itemizing the other must itemize as well, even if the standard deduction is more favorable. 

Typically, married filing separate filers choose the standard deduction but in some cases there are enough itemized deductions for both.

To figure the adjustment, 

1. After entering the income items per the forms, note the adjusted gross income on form 1040, line 11. 
2. Then outside of TurboTax calculate and split the income as noted above.  
3. Next use the "Search" function at the top right
4. Search for "Community Property" 
5. Use the "Jump to" link in the search results to get to the "Community Property Adjustment" interview.  
6. Enter the appropriate plus and minus amount on each return.  

This is the adjustment that affects the tax calculations. 

The only other adjustment that you could enter to affect tax calculations is a withholding adjustment, if you wish. Again, whatever plus adjustment you make on one return a corresponding negative adjustment goes on the other return.  

The other entries showing income splits are informational only to support the actual adjustments and do not affect tax calculations.