Start from what the goal costs today. It will cost more by the time you need it, especially education, whose costs rise faster than general inflation. The planner inflates the cost, grows what you have already saved, and works out the saving that closes the gap.
How it is worked out
Future cost = C × (1 + inflation)t. Monthly saving = gap ÷ what ₹1 saved every month grows to at your return.
Questions
What return should I use?
Match it to the time left: equity-like returns for 7+ years, debt-like returns (6-7%) for goals within 3-5 years.