Is there a legal limit on rent increases in India?
Unlike some countries, most Indian states don't cap residential rent increases by law — the Rent Control Acts that do exist mostly cover older, pre-regulation tenancies and rarely apply to typical open-market rentals today. In practice, the increase is whatever both parties agree to, usually set out in the rental agreement itself.
Why 5-10% a year?
It's not a rule, but a widely-used convention — many standard rental agreements (including ones generated by this site) build in a 10% increase at each renewal, roughly every 11 months, to keep pace with inflation and area-level rent trends. A hike well above that is worth discussing with your landlord, especially if the local rental market hasn't moved much.
What can I do if an increase feels too high?
Check what similar properties in your area are currently renting for, and simply ask your landlord to explain the basis for the hike — a long, reliable tenancy is often worth a modest compromise to a landlord who'd rather avoid the cost and uncertainty of finding a new tenant.