Washington ? Numbers have always defined Richard Semmler.

A 59-year-old mathematician, he teaches calculus and algebra at Northern Virginia Community College.

He can explain how to find the derivative of a polynomial and solve complex equations.

But in his private life, Semmler has reduced his existence to the simplest equation.

In the past 35 years, by working part-time jobs and forgoing such everyday comforts as a home telephone and vacations, by living in an efficiency apartment and driving an old car, Semmler has donated as much as half of his annual income or more to charity.

His goal: $1 million before he retires.

“If I didn’t do all of the things I was doing, I would probably have a new car every two years and I would have a huge house with a huge pool,” Semmler said this week as he took a break from pounding nails on a Habitat for Humanity house in Vienna, Va. He donated $100,000 to this house, most of the money required to build it.

Percentage-wise, Semmler’s generosity is exceedingly rare among the middle-class – or the rich, for that matter, say those who study philanthropy. Each year, U.S. households give away an average of 2 percent of their income to nonprofit and religious organizations, according to Giving USA, which tracks donation trends.

A household with Semmler’s annual income, $100,000, donates an average of $2,000 annually to charity. Last year, Semmler gave away $60,000.

By the end of this year, by Semmler’s calculations, the total will be slightly more than $770,000.