Let's say you want to start working out, and want to motivate yourself by tracking progress.

Only measuring your weight won't cut it - you could become a gym rat overnight, and get ripped, but your weight might not change much, and neither your BMI. How would you even know when to stop? When is your body "good enough"? What if you become too ripped, car drivers start staring at you, and you start causing car crashes? It's dangerous.

One solution to this problem is ABSI - A Body Shape Index. In addition to measuring your weight, also input your height and waist circumference, and you can get a score that is closely related to your health. While BMI can't tell a muscly person from a couch potato, ABSI uses the waist circumference to do so.

Subtract the average ABSI for your sex and age, and divide by the standard deviation, and you get the ABSI z-score, which is what you need to look at. Generally, if it's zero or below, you're pretty fit. My personal target is -0.75, but if I get to -1 it's OK. I get random day-to-day variations of 0.2-0.3 anyway. I should probably draw a moving average instead of the data itself. I'll get to it eventually.

To improve the score, you need to lose fat (by avoiding too many calories), build muscle (by working out), or both.

• To avoid calories, I stuff myself with healthy, water-rich food. Veggies, fruit, legumes, greens and such. After that I feel too full to crave energy-dense foods.
• To work out, I follow the "What, Me Exercise?" chapter of Hacker's Diet. At least ostensibly.

You can also improve your score by sucking your stomach in, but that is cheating. So is pulling the measuring tape tight or rounding to a convenient n. If you want a more accurate method, here it is.

You can record your data here, and this calculator will make a nice chart and remember your history in the browser's local storage. You can also get a TSV file. The ABSI is recalculated on import. This calculator has no server component, so you can save the page and linked scripts ("Web Page, complete" in Firefox) and keep it forever on your own device, in case my server goes down.

Update 2025-06-24: I use some voodoo magic to guesstimate your age at death (essentially a life table crammed into a formula). I didn't test it too much; don't be surprised if it has greater than 10% error. But I think it's useful for judging how much a tiny change can impact your life. In one month I progressed enough to win 5.9 extra years of life, with not much effort, going from a z-score of 0.983 to 0.588.

Update 2025-06-26: Fixed error when there is no history. There was too much validation going on.