Each of these items effect one another and by playing around with them you can find out if your current savings plan will or will not work, and, if not, what you need to do to make it work.
For example, if you decrease the time you have to save, you are going to need to put away more each month. On the other hand, if you start putting away more than you expected, you will reach your savings goals sooner than expected. Unlike the others, taxes are not something you can alter to achieve your savings goals.
Play around with this calculator to see if you are on the right track.