A commonly used starting estimate is the 25x rule: multiply your expected annual expenses in retirement by 25, which assumes a roughly 4% safe annual withdrawal rate from your corpus. If you expect to spend ₹6 lakh a year in retirement (in today's money), that suggests a corpus target of around ₹1.5 crore, adjusted upward for inflation by the time you actually retire.
This estimate needs real adjustment for the Indian context: healthcare costs tend to rise faster than general inflation as you age, and joint family support structures that once reduced retirement costs are less common now, so many financial planners suggest being more conservative than the 25x rule alone would indicate, especially for healthcare.
The other major variable is retirement age and lifespan — retiring at 55 and living to 90 requires a meaningfully larger corpus than retiring at 62 and planning for 80, purely due to the extra years the money needs to last. The Goal Planner and NPS calculators on this site can help translate a target retirement corpus into the monthly investment needed to get there from wherever you're starting today.