I suggest you go for a simple payroll software that will solve all your troubles. While we have Excel formulas, I recommend opting for software such as Tally or other economical alternatives. Choose a vendor who has been in this business for at least 10-15 years, with a good support team, and who provides regular updates on tax changes.
Investment Declaration and Tax Deduction Process
Typically, at the beginning of the financial year, around April/May '13, companies collect what we call an "Investment Declaration Form" for advance tax calculation from staff members falling under taxable income. No proofs are required at this stage, but it must be submitted compulsorily around January-February '14.
Based on the above declaration, the Finance department will compute the taxable income and deduct the same amount every month. If a staff member fails to submit the proof by January/February '14, the balance tax will be deducted between January-March '14.
Good luck.
Regards,
Ukmitra