Not familiar with all the acronyms so...what do you get if you take expected annual expenses, subtract expected annual guaranteed income, then divide by expected investment balance?

For all those "expected" numbers, use whatever you deem reasonable for inflation, investment returns, etc. between now and the retirement date you pick, and do the calculation as of that retirement date.

If you can assume expenses and guaranteed income both increase at the same inflation rate, their difference will also increase at exactly that rate - and that is what the "4% SWR" analysis assumes. You can compare your division result to that 4% and get some idea of how safe or risky that retirement date would be.

If expenses and guaranteed income will not increase at the same rate, you are getting outside the bounds assumed by simple methods, and may need to use

www.cfiresim.com or other retirement analysis package.