[edtost]

assume (year(i) withdrawal) = (year(0) expenses) * (1 + inflation%)^i

the easy way to do this is to assume that you want to maintain the same level of inflation-adjusted wealth at the end of each year, with the balance going to your kids or whatever at death.

assuming constant values for return and inflation, we get an infinite-horizon problem in terms of our assets:

a_{t+1} = (a_t-w_t)*(1+r)

a_t*(1+i) = (a_t-w_t)*(1+r)

a_0*(1+i) = (a_0*(1+r)) - (e_0*(1+r))

a_0*((1+r) - (1+i)) = e_0*(1+r)

a_0*(r-i) = e_0*(1+r)

a_0 = (e_0*(1+r)) / (r-i)

so if we assume r is something like 5%, i is close to 3%, and initial year expenses of $24k, your starting endowment should be

a_0 = (24000*1.05)/(.05-.03) = 25200/.02 = $1.26M

edit: note: this assumes a tax-free world, so r should be after-tax return and e_0 should be the amount of pre-tax income one would need to net living expenses in year 0. adjusting the numbers above for an effective tax rate of 30% gives

a_0 = (25200/.7)/(.05*.7-.03) = 36000/.005 = $7.2M

which is a big difference.