Every investor has different cash flow structure and most often a combination of regular cash flow and some periodical lump sums to invest.
This again is a simple excel sheet to help to figure out how much it takes on a monthly / annual basis to reach a given financial goal at a given return.
Also this sheet helps to understand the inflation and tax effects on investment returns.
For eg,, an investment yielding 9% returns after the investors tax bracket of 30% may actually yield only [9-2.70] 6.30% net returns which is the number to look for persons in high tax bracket.
Similarly if the cost of child education today is 3 Lakhs and one is planning for this 18 years from now at an assumed inflation level of 7% the future cost would be around 12 Lakhs.