Seeking Help Trying to figure Airtel's calculation

[iDJ]

If a user recharges on 13th December 2020. 28 days from 13th December according to google is 10th January 2021. How is plan on Airtel expiring on 9th January 2021? Where did the extra day go?

 

[Abhinav]

Because plan started from 13th itself, if you count number of days including recharge date it will be 28 on 9th January.

 

[Naimish555]

IDJ bro,
Once your package active on day (13-12-20) then it count as 1 day & remaining 27 days are Completed on 9th January (count as 28th Day).