How much you save depends on the lifestyle you have now, whether you want to maintain that lifestyle here and how much you make. To determine that you need to know what kind of lifestyle you expect. i.e.
4 b/r 2600 sq ft
2 kids - private schooling
1 car
eat out 3x week
1 vacation to the US every year
2 regional vacations every year
alcohol/smoking (expensive vices here)
Also
Who pays your taxes?
A typical family of four making US$150k per year in the US with 2 kids in SAS will need to make in the range of $350-400k sing for parity. Here is a typical budget:
Housing - 7,000/mo
Car - 2300/mo
Util - 1200 / mo (detached or semi d with a/c) includes mobile & moderate o/seas calls
groceries - 1200 / mo
maid - 800 / mo
entertainment - 2,000
Annual Expenses
Schooling X 2 = 40,000
Home leave X 4 = 18,000 (tix + expenses)
Regional vac X 8 = 7,000
Savings goal = 50,000 (this is low IMO)
Call it 290k per year or 180kUSD
Tax Fed US
70k exclusion
110 * .30 = 33k
State
110 * .1 = 11k
So about 43k for taxes in the US
Singapore (in USD)
180k * .1 = 18,000
You have to gross up the tax due because if you get it in pay it will also be taxed.
So you need about US$250k.
Note this is a wild ballpark - you can, of course, choose to live completely diffrently