If you hated math, then calculators were your best friends. That hasn’t changed for the adults in us. From the ancient abacus to the latest smartphone app, the humble calculator has helped you keep track of large numbers. But thanks to the web, a calculator isn’t always about math or arithmetic. Here are five useful but cool online calculators that can help you stay on top of your time, habits, sleep, and life itself. Free Time Calculator: Visualize Your Free Time About 40% of our time is spent sleeping.