Erhard Weigel (16 December 1625 – 20 March 1699) was a German mathematician, astronomer and philosopher.

He concurred with Jakob Ellrod's "Mittel-Calendar",[4] and with the advocacy of Leibniz and others, that the date of Easter should be based on the astronomical measurement of the spring equinox and the next full moon.

He followed Jakob Ellrod to the Imperial Diet in Regensburg to advocate the use of the Mittel-Calendar or New Gregorian calendar.

[3] Through Leibniz, Weigel is the intellectual forefather of a long tradition of mathematicians and mathematical physicists that connects a great number of professionals to this day (see Academic genealogy of theoretical physicists: Erhard Weigel).

The Mathematics Genealogy Project lists more than 50,000 "descendants" of Weigel's, including Lagrange, Euler, Poisson and several Fields Medalists.