How is percentage of social security tax determined once over the limit?

Answer 1

Excess Social Security or Railroad Retirement Tax Withholding
Most employers must withhold social security tax from your wages. The federal government and state and local governments in some cases do not have to withhold social security tax from their employees' wages. If you work for a railroad employer, that employer must withhold tier 1 railroad retirement (RRTA) tax and tier 2 RRTA tax.

Once the limit is reached for the year, the employer can stop withholding it

Two or more employers. If you worked for two or more employers in 2005, too much social security tax or RRTA tax may have been withheld from your pay. You may be able to claim the excess as a credit against your income tax when you file your return. Table 3-1 shows the maximum amount that should have been withheld for any of these taxes for 2005. Figure the excess withholding on the appropriate worksheet on page 46.


Table 3-1. Maximum Social Security and RRTA Withholding for 2005

Type of Tax Maximum wages subject
to tax Tax rate Maximum
tax to be
withheld
Social security $90,000 6.2% $5,580.00
Tier 1 railroad retirement (RRTA) $90,000 6.2% $5,580.00
Tier 2 RRTA $66,900 4.4% $2,943.60


Joint returns. If you are filing a joint return, you cannot add any social security or RRTA tax withheld from your spouse's income to the amount withheld from your income. You must figure the excess separately for both you and your spouse to determine if either of you has excess withholding.

Answer 2

There's a worksheet to calculate it on page 28 in the instructions for the 1040 form. You can download it at irs.gov or pick up a copy at your local post office or public library.

Answer 3

There is no social security tax once you are over the limit.

So it goes to zero.

I think you need to rephrase your question. I don't understand what you are asking.