DO NOT enter withholdings from any income statements such as W2, 1099, etc. in this section. (This mistake would either cause your return to be rejected by the IRS or accepted and a letter later mailed to you stating you owe this money back along with penalty and interest amounts.) You must enter those withholdings in the appropriate INCOME section of the online interview.
Enter any estimated federal income tax payments you made. Include any overpayment from return that you applied to your estimated tax for this year.
If you and your spouse paid joint estimated tax but are now filing separate income tax returns, you can divide the amount paid in any way you choose as long as you both agree. If you cannot agree, you must divide the payments in proportion to each spouses individual tax as shown on your separate returns for the prior year. For an example of how to do this, see Pub. 505. Be sure to show both social security numbers (SSNs) in the space provided on the separate returns. If you or your spouse paid separate estimated tax but you are now filing a joint return, add the amounts you each paid.
For more information, see Page 47 of Form 1040 Instructions.