The verbiage is completely incomprehensible to me. I don't understand the distinction between Pension vs Off chart. If it is additional income, its a positive number, starting in the year entered. If it is additional spending, a negative number.
Don't understand any difference between "portfolio withdrawal" and "ordinary lifestyle." "will not be shown in the annual spending chart that will be shown in the results." -- What spending chart?
It's a way to fine tune FIREcalc if you know your spending is going to significantly and permanently change in the future.
For example, let's say that I spend $40,000 per year today. Included in that $40,000 is $1,000 a month in child support for my 8 year old, and that child support ends when the child turns 18.
If I put in $40,000 a year as spending, then FIREcalc will overestimate how much I need to have, because it assumes I need to spend that amount for the rest of my life.
But I probably shouldn't ignore the $120,000 in pending child support payments over the next 10 years either.
So I put in $40,000 a year as spending, and then enter an "off chart spending reduction" of $12,000 per year starting 10 years from now. Since child support doesn't change with inflation, I uncheck the inflation box.
Now FIREcalc can do the runs with 10 years of $40K and the rest of the time period (30 years or whatever I choose on the first tab) at $28,000.
...
Basically any time you will have a significant and immediate increase or decrease in spending that you're willing to count on, you can use this feature.
Other examples might include paying off your mortgage, or the start of a pension, or the decision to start skydiving at age 80, or whatever.