22 August 2012
Tax is deducted when salary is paid to you if it is monthly then monthly deduction if qtrly then qtrly deducted.
calculate tax on your income for the year based on the best avaialable info divide it with 12 if TDS is to be ascertained for 1st month. If TDS is to be calculated during year then total tax for the year less TDS already deducted and divide the tax by balance number of months.