The unit you actually plan in
Most of us don't plan our lives in years. We plan them in weekends. The hike, the visit, the long breakfast, the afternoon you finally fix the bike: they all live on Saturdays and Sundays. So it's worth knowing how many of those you have. For someone in their mid-thirties planning for 80, it's around 2,300. That sounds like plenty, until you notice how many go to errands, recovery and things you didn't choose.
How it's calculated
We count every Saturday between today and the date you'd turn the lifespan you choose (80 by default). Each Saturday stands for one weekend. "Left this year" counts the Saturdays from today to December 31. The chart draws one row per calendar year: this year's weekends in amber on the first row, then a full row of about 52 for each year after. Everything is computed in your browser.
Like every number on this site, the lifespan is a choice, not a forecast. Recent US life expectancy estimates sit in the high 70s; that is an average across a whole population, and your own situation will differ. Plan with whatever number helps you.
Spend a few on purpose
While we are postponing, life speeds by.Seneca
The easiest way to waste a weekend is to never decide what it's for. One simple practice: look at the number of weekends left this year, and pick a handful to name in advance. One for a person you've been meaning to see. One for the thing you keep saying you'll start. One left completely empty, on purpose. Naming the when and the what, which psychologists call an implementation intention, roughly doubles the odds you'll actually follow through.
The rest can be as lazy as you like. Not every weekend has to be optimised. The point is only that some of them should be chosen.
Want a bigger unit? See your summers left. A smaller one? Your days left, ticking live.
Keep the count in view
Days Unspent puts this idea on your desktop: the days you have left to spend, your weeks as a spiral, and the one thing you're working on, in a live wallpaper for Mac and Windows. The count on this page is free. The wallpaper is $29, once.