One thing to keep in mind is that your income, hopefully, will not stay stagnant over the next ten years. Therefore, you should also factor into your calculations what you think your income will be over the next ten years. It is highly likely that even if you are not saving the full 4000+ a month today, if you are able to make some current expense improvements, and factor in salary raises, that you can get closer to that 750,000 then you think right now. You did not mention what your actual expenses and budget are like, but if they are around that $25,000 that you mentioned, and factoring in Income growth of 5% a year and Expense growth of 2% a year, and 7% investment returns you will end up at over 700,000 by year 10. See diagram below. If your current expenses are $3000 a month you will still end up with over $500,000. You also didn't mention what your current debts are so you will have to factor that into the equation as well. In summary, if you are aggressive in reducing and keeping your expenses down, and keep working on increasing the income side of the equation, you are well positioned to accomplish your goals in 10-15 years. Also, if your wife starts to work part-time while the kids are in school, you could also boost the income side of the equation and put all additional income towards debt and/or savings.
Income Expense Monthly Annual Cumulative
Savings Savings Savings
Year 1 5,300 2,083 3,217 38,600 38,600
Year 2 5,565 2,125 3,440 41,280 82,582
Year 3 5,843 2,168 3,676 44,109 132,472
Year 4 6,135 2,211 3,925 47,095 188,840
Year 5 6,442 2,255 4,187 50,245 252,304
Year 6 6,764 2,300 4,464 53,569 323,534
Year 7 7,103 2,346 4,756 57,076 403,258
Year 8 7,458 2,393 5,065 60,774 492,260
Year 9 7,831 2,441 5,390 64,675 591,393
Year 10 8,222 2,490 5,732 68,787 701,578