How does the countdown work?

Enter a future date and optional time; the timer shows the time remaining and updates every second.

Online Countdown Timer

Count down to a target date and time. See days, hours, minutes, and seconds remaining.

Target date

Time (optional, HH:MM)

How does the countdown work?: Enter a future date and optional time; the timer shows the time remaining and updates every second.

Celsius to Fahrenheit Converter

Convert Celsius to Fahrenheit and Fahrenheit to Celsius instantly. Free temperature converter.

Tip Calculator

Calculate tip and split the bill. Enter bill amount, tip percentage, and number of people.

Roman Numeral Converter

Convert numbers to Roman numerals and Roman numerals to numbers. Supports 1–3999.

Combinations Calculator

Calculate C(n,r) — the number of ways to choose r items from n without order. Uses n!/(r!(n-r)!).

Combinations with Replacement Calculator

Calculate the number of ways to choose r items from n with repetition allowed. Formula: C(n+r-1, r).

Even Permutations Calculator

Count how many permutations of n objects are even (expressible as an even number of swaps). For n ≥ 2, equals n!/2.