You are learning what every retiree learns, that a small change in assumptions is the difference between caviar and being destitute.
I spent the first year of my semi-retirement running numbers through every calculator, spreadsheet and program there is anywhere and everywhere to try and better understand the sensitivity of different parameters. I particularly liked portfolio visualizer. It was worth $250 per year.
Here are a few of the conclusions:
1. Inflation - I settled on 3% for a conservative number and 2% for optimistic. I figured that if it runs 4%, other asset returns will eventually return higher rates leaving the same real returns as inflation running 3% or less. That might not be a good assumption but it’s the only way to sleep at night.
2. Returns - think simple. First decide on your tolerance for risk, which will give you a stock bond asset allocation percentage. For example, 60/40 is the typical in retirement ratio. Then take some conservative and optimistic return rates for each and calculate the mixed value. Say conservatively 4% for bonds and 7% for stocks for a combined 5.8% return. Optimistically 4.5% for bonds and 9% for stocks, for a 7.2% rerun. Plug those numbers into the calculators and see if it works.
3. Simulations - In Monte Carlo simulations, which are critical, a financial planner will often say you need an 80% or better probability for success. I prefer 90% + .
4. Income - to reduce sequence of returns risk, look at how much cash the portfolio generates each year on average and compare it to your expenses. I prefer to have enough income to cover most of my expenses so that I don’t have to sell stocks in a down period when prices are depressed. However I am always total return cognizant. I don’t want a lot of high dividend yield investments with poor overall returns. Unfortunately right now I do have some investments that fall into that category. If and when rates drop I will jettison some of that.