When you become divorced or separated, you will usually have to file a new Form W-4, Employee's Withholding Allowance Certificate, with your employer to claim your proper withholding allowances. If you receive alimony, you may have to make estimated tax payments.
If you do not pay enough tax either through withholding or by making estimated tax payments, you will have an underpayment of estimated tax and you may have to pay a penalty. If you do not pay enough tax by the due date of each payment, you may have to pay a penalty even if you are due a refund when you file your tax return.
For more information, see Publication 505, Tax Withholding and Estimated Tax.taxmap/pubs/p504-007.htm#en_us_publink100044297
If you and your spouse made joint estimated tax payments for 2008 but file separate returns, either of you can claim all of your payments, or you can divide them in any way on which you both agree. If you cannot agree, the estimated tax you can claim equals the total estimated tax paid times the tax shown on your separate return for 2008, divided by the total of the tax shown on your 2008 return and your spouse's 2008 return.
If you claim any of the payments on your tax return, enter your spouse's or former spouse's social security number in the space provided on the front of Form 1040 or Form 1040A. If you were divorced and remarried in 2008, enter your present spouse's social security number in that space and enter your former spouse's social security number, followed by "DIV" to the left of Form 1040, line 63, or Form 1040A, line 39.