Smart calculators
for everyday life

Race time predictors use the Riegel formula to project a marathon or half marathon time from a recent 5K. Here's the real math, why big jumps drift, and how fall marathon training season should read the number.

Weighted grades don't average the way most students assume. Here's the exact formula for what score you need on your final exam, with a real worked example.

A pregnancy due date isn't a prediction of birth day — it's a 40-week estimate from your last period. Here's the real math behind Naegele's rule, ultrasound dating, and why the date moves.