Save $3500 monthly when I turn 30

One of my assumptions in accumulating "$500,000 by 33 years old" was "My wife and I will save at least $2500 monthly combined($30,000 yearly) from age 28 to 30 and $3500 monthly($42,000 yearly) after I turn 30" 

To save $3500 monthly from the age of 30 onward, I assume a combined monthly income of $8,000. Also,  household expenses are included as my HDB flat will be ready by then.