A more precise model still might be to try to factor in the expected loss in healthy years for the donor, and the average lifespan gain of a kidney recipient.

A more precise model still might be to try to factor in the expected loss in healthy years for the donor, and the average lifespan gain of a kidney recipient. If you pull a child out of the way of a speeding truck, you've saved their life without losing any quality of life for yourself or for them. That's a "perfect" life save. Organ transplant is more subtle. If you already plan to donate your kidneys at death, donating one of them when younger seems less obviously good. It'd seem worthwhile to build a more detailed model before going through with it.