How much savings do you need NOW to retire with basic living in Singapore?

In my previous post, I estimated that the basic no frail cost of living in Singapore as of now for an old couple = S$1348 per month. 

So, how much does a couple need to retire for 30 years from now if they just need S$1348 per month for living expenses and assuming investment return of 3% per year/annum (p.a.) on their capital and inflation of 2% per year?  Note that my assumption has 2% p.a. increase in expenses built-in year after year (and not a flat S$1348 pm). 

According to my calculation, the couple just requires a lump sum of S$420,000 to be able to retire now for 30 years! 

Question 1: Is average investment return of 3% p.a. realistic?
A: Yes, 3% is already considered low. Don't forget Singapore Government gives 4% for your CPF Special Account and Medisave.

Question 2: Is average inflation 2% p.a. realistic?
A: This will depends on global economic situation and more importantly government's economic and monetary policy, especially when Singapore uses exchange as a tool to control inflation.  Also, Singapore government has great control over medical costs via their economy of scale in operating all gov hospitals and polyclinics.