I came to US on May 30 2010 on L1 visa and wy wife arrived on sept 3rd.I kept marriage status box as single and allowances as 3 on W4.is this correct?
Please help me in understanding the difference between filing returns and W4.
Do I need to change the W4 or wait until the filing returns.

QUOTE," . . . and wy wife arrived on sept 3rd. "----No. You should check "married" on line #3, not "single".

" I kept marriage status box as single and allowances as 3 on W4.is this correct?"--- It depedns on a situation. For instance, suppose your spouse does not work in the US and you have onkly one job, then you can claim one personal allowance on line B. If your spouse works and have more than one job, then you can claim one more personal allowance on line c, so you can claim totally three personal allownces on your W-4 as long as you satisfy all the requireemnts(conditions as suggested above); one on line A,B ,and C.

Basically, as you can see, you use Form W-4 to figure the right amount of federal and state tax( if applicable), and even your FICA taxes, as a L1 visa holder, to have withheld from your paycheck.

Thanks wnhough.
Do I need to update W4 with the updated status or I can wait till the tax filing so that I can get better refund.
Which one is correct?
This is my first visit to US,so I have lot of confusion about this.

QUOTE," Do i need to update W4 with the updated status or . . ."---Yes. File your amended W-4 and give it to your employer( contact your employer). As your marital status( from single to married) or the number of your withholding allowances have changed, you need to file an amended W-4. Suppose there is a decrease in the number of your allowances, then you must furnish your employer with a new certificate within 10 days. If there is an increase in the number of your allowances, then you can either file a new certificate or just allow the current certificate to remain in effect.
Your employer makes the certificate effective no later than the start of the first payroll period ending on or after the 30th day from the date the replacement Form W-4 is received from you.
"i can wait till the tax filing so that i can get better refund."----As you know, the withholding allowance is related to, but not the same as, the number of dependents you can claim on your tax return.What I am saying is that the number of withholding allowances on your form W-4 may differ from the number of exemptions claimed on your tax return.
Your employer uses your W-4 in his hand to withhold your quarterly estimated Federal taxes. Basically, it is up to you; as you claim more withholding allowances on your W-4, you will pay less quarterly estimated Federal taxes and you probably pay additional tax on your federal tax return when filing 1040or 1040a/ez.
Also, REMEMBER:By December 1 of each year, your employer has to remind you to turn in a new form for the next year if your marital status or number of allowances has changed. Your employer is also required to start using any new W-4 you turn in within a month of getting it from you.

Thanks wnhough.
At present my number of allowances in my W4 is 3 (A,B,C) and marries status as single.
So what happens if I don't change W4 now and file the taxes with the updated information as married.

Nothing happens, except that more funds are withheld for taxes than is required. You will get the overage back (in the form of a refund) when you file your tax return.

Agreed.

Thank You for the valuable answers.