How do you calculate weighted average number of shares?

Weighted average shares = total number of shares remains outstanding during year divided by number of months

For example: during first 6 months total outstanding shares are 100000

on 1st July company issues 100000 more share

Now total shares = 200000

SO weighted average share = (100000 * 12 + 100000 * 6)/12

weighted average shares = 1800000/12 = 150000

OR

weighted average shares = (200000 + 100000) /2 = 150000