I have a spreadsheet showing current and projected expenses and income for the next couple of decades. I use it to remind myself why I'm nowhere near retirement.

One of the columns is projected routine spending, which is current routine expenses like insurance, taxes, bread and milk, plus projected increases in routine spending (ie, things we don't pay for now, but I assume we will have to in the future, like health care premiums). Since costs rise, year to year, I add a percentage increase, just for inflation, each year.

A second column is projected extraordinary expenses -- new cars and the like.

Last night, I thought 'why separate out projected changes in routine from extraordinary? Both are money we expect to spend, and both are limited in how often we'll have to pay -- they don't go on forever. ' So I changed the projected routine spending to be just that, and changed projected extraordinary to be just projected one-time spending. Hey, what's the diff, right? Just cleaning up the spreadsheet.

Oh, my goodness.

It turns out that by combining the one-timers with the normal spending, I was making the implicit assumption that the one-timers would actually happen in whatever year they occurred -- and every year thereafter. Once I pulled them out, so that they don't get rolled up each year, the spreadsheet projected our total spending over the entire period to be about 70% of what it otherwise would have been. And the net effect is, our projected ending net worth is projected to be about 15% higher.

Maybe I will retire.