X*((1+i)^m-1)/i+C*(1+i)^m

A Lifehacker post begins this way:

If 1 million dollars isn’t enough to retire anymore, the obvious question becomes: What is?

I’m obviously in the wrong line of business for this discussion – or maybe just the wrong line of business to retire. One of the commenters offers the formula in the title:

X =monthly contribution
i = monthly interest (assume 8% annual, then i = .00667)
m = months until retirement
C = current nest egg

The article refers to this Get Rich Slowly website.