As kalpna rightly said 1Pl is given for every 20 working days which may come out to apps 18.25(365/20) but to avoid the complexity of how many days were working and how many non-working, companies directly give 21 days or 30 days depending on the company policy. This can also be given as 1.75 or 1.5 days per month which gets accumulated every month in employees PL account.
Company is bound to give the minimum leave as per the order but the no of leaves that can be carried forwarded does not have a limit. So it is at the sole discretion of management of the company to define how many leaves should be carried forwarded and how many enchased. Since PLs are liability on the company’s account, some company prefer to motivate their employees to enchase their leaves at the end of calendar year.
In my current company the policy is that, out of every 30 pl credited in the employees account 15 have to be availed and rest 15 will have to be carried forwarded. the maximum accumulation of this pl is 300 days. This has two positive effects
1. Employee will try not to avail 15 leaves so will be present in the company
2. After 20 years in same company his PL accumulation will be 300. Now at the time of retirement this pl will be a big financial help to the employee since the calculation of entire 300 pl will be done on his current ctc which will be much much more then what he was getting 20 yrs back.