I am working in an MNC and am investing into Employee Stock Purchase Program (ESPP). During the purchase of the share there is a 15% discount given on the least value of the 1dt and last date of the ESPP offering period. My finance department has confirmed that the tax is deducted as per my slab ie 30% (shares equivalent to my gain due to 15% employee discount and increase in the value per share from the starting date to the date of vesting) . E.g. out of 100 shares purchased, about 20 shares were sold off to recover for 30% tax on the effective gain.
My question is whether I need to pay any tax on the gain again during ITR filing on the gain. If yes, how much? If no, what all documents I need to keep ready to convince the authority that the no tax is due on this?