Two calculations, not one
Retirement planning asks how large a corpus can pay you an inflation-adjusted income for as long as you live, and then what you must invest each month to build it.
The corpus figure here assumes your expenses rise with inflation every year of retirement, and that the balance stays invested at the more conservative post-retirement rate. Money you are drawing on should not be invested as aggressively as money you are still adding to.
What to subtract before you start
Any pension, EPF, NPS or annuity you are already entitled to reduces what you must build yourself. Enter what you have accumulated so far, and treat a pension as reducing the monthly income figure you enter above.
Medical costs deserve a separate line. They rise faster than general inflation and arrive precisely when income has stopped.