Formula
Remaining days * (New package price / Old package price)
Example
- Current package: 250 subs (100 remaining days)
- Wants to upgrade to 500 subs package
- 250 subs price: 160$, 500 subs price: 320$
Formula for new remaining days = 100 * (320/160) = 50 remaining days.
After package upgrade to 500 subs, the new expiry will be adjusted to 50 remaining days.