The costs associated with treating these ills are enormous. A startling study published in July in The Lancet looked at data from 142 nations about time lost from work, insurance claims, health care billing, and other costs that the researchers determined were most likely caused by people being sedentary and now suffering from heart disease, stroke, Type 2 diabetes, breast cancer or colon cancer. Each of these conditions is believed to be much more common among people who do not exercise.

The study concluded that inactivity costs the world economy almost $68 billion annually in medical expenses and lost productivity. In the United States alone, the total was almost $28 billion. Most of the global costs were borne by governments and businesses, the authors write, but almost $10 billion worldwide was paid out of the pockets of individuals.

But those kinds of aggregate numbers, while concerning, are also abstract. They don’t tell us how much each of us, individually, might be paying out or saving in future health costs when we decide either to go for that walk at lunchtime or skip it.

So for the new study, the researchers set out to quantify the value of exercise for each individual.

To do so, they first turned to a huge storehouse of data about what we spend on health care. The annual Medical Expenditure Panel Survey, which is conducted by federal agencies, asks a large, representative group of Americans what they have spent on health care in the past year. The survey includes detailed questions about insurance coverage, prescription costs, doctor visits, hospitalizations, medical devices, other out-of-pocket spending, reimbursements, and so on.