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Stock-based compensation (Tables)
12 Months Ended
Mar. 31, 2021
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions
The fair value of options has been estimated on the dates of each grant using a binomial option pricing model with the following assumptions:
 
    
Years ended March 31,
    
2019
  
2020
  
2021
Dividend yield
  
0.62%-0.65%
  
0.61%-0.85%
   0.61%
Expected volatility
  
14.53%-18.68%
  
15.30%-20.13%
  
20.13%-28.93%
Risk-free interest rate
  
7.23%-8.31%
  
5.81%-6.70%
  
4.63%-5.75%
Expected term (in years)
  
2.78-5.16
  
2.82-5.42
  
2.65-5.43
Schedule of Share-based Compensation, Stock Options, Activity
Activity in the options available to be granted under the Employee Stock Option Scheme is as follows:
 
    
Number of options available to be granted
year ending March 31,
 
    
2019
    
2020
    
2021
 
Options available to be granted, beginning of period
     235,683,200        202,413,370        159,487,350  
Equity shares allocated for grant under the plan
                    
Options granted
     (39,790,000      (47,773,600      (57,466,600
Forfeited/lapsed
     6,520,170        4,847,580        2,673,420  
    
 
 
    
 
 
    
 
 
 
Options available to be granted, end of period
     202,413,370        159,487,350        104,694,170  
    
 
 
    
 
 
    
 
 
 
 
Activity in the options outstanding under the Employee Stock Option Scheme is as follows:
 
    
Years ended March 
31
,
 
    
2019
    
2020
    
2021
 
    
Options
   
Weighted
average
exercise
price
    
Options
   
Weighted
average
exercise price
    
Options
   
Weighted
average
exercise price
 
Options outstanding, beginning of period
     150,887,600     Rs. 525.11        136,612,822     Rs. 682.99        142,865,602     Rs. 899.03  
Granted
     39,790,000       1,030.24        47,773,600       1,220.13        57,466,600       1,235.80  
Exercised
     (47,544,608     462.89        (36,673,240     504.10        (29,490,022     596.85  
Forfeited
     (6,410,770     759.21        (4,813,580     965.64        (2,032,110     1,163.29  
Lapsed
     (109,400     418.55        (34,000     568.10        (641,310     929.57  
    
 
 
   
 
 
    
 
 
   
 
 
    
 
 
   
 
 
 
Options outstanding, end of period
     136,612,822     Rs. 682.99        142,865,602     Rs. 899.03        168,168,760     Rs. 1,063.79  
    
 
 
   
 
 
    
 
 
   
 
 
    
 
 
   
 
 
 
Options exercisable, end of period
     80,609,722     Rs. 508.89        64,464,392     Rs. 638.18        64,453,260     Rs. 834.48  
Weighted average fair value of options granted during the year
           Rs. 262.79              Rs. 305.78              Rs. 320.42  
Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range
The following summarizes information about stock options outstanding as of March 31, 2021:
 
         
As of March 
31
2021
 
Plan
  
Range of exercise price
  
Number of
shares arising
out of options
    
Weighted
average
remaining life
(years)
    
Weighted
average
exercise price
 
Plan C
   Rs.417.75 (or US$ 5.71)      9,700        0.32        417.75  
Plan F
   Rs.417.75 to Rs. 731.08 (or US$ 5.71 to US$ 10.00)      34,974,270        1.48        610.67  
Plan G
   Rs.882.85 to Rs. 1,235.80 (or US$ 12.07 to US$ 16.90)      133,184,790        3.18        1,182.83