Hi,
Look at expenses
Rent 2000 pm
School fee 2000 pm (in International school, Even Singapore schools will charge at least 500 pm as you are a foreigner)
Tax 900 pm (15% is the tax rate)
Food, TV, elec, internet, mobile, etc
1500 pm
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This alone is SGD 6400 pm. What about some savings, movies, eating out, etc? I suggest you ask for at least SGD 9000 per month. Or come and live alone in Singapore with 4 other guys in a single room. Of course, all this will apply after you get EP which is doubtful these days at a salary of SGD 6400.