Time Calculator

You may use this calculator to “add” or “subtract” two different time measurements. You can leave the input sections blank, which will result in a default value of zero.

Subtract or add time from a given date

Use the Time Duration Calculator to compute the time between two dates. Try this calculator to add or subtract time from a beginning time and date. Depending on the time deducted or added, the new time and date will be the outcome.

Calculating Time with an Expression

This calculator can add or subtract two or more time points with an equation. The following are acceptable inputs: d, h, m, and s. D represents days, h represents hours, m represents minutes, and s represents seconds. The only proper functions are + and -. A proper formula would be “1d 2h 3m 4s + 4h 5s - 2030s.”

Time, like other variables, can be added or removed. But there is a difference in computing with decimal and time units. The table below shows several popular units for measuring time.

Unit	Definition
millennium	1,000 years
century	100 years
decade	10 years
year (average)	365,242 days or 12 months
common year	365 days or 12 months
leap year	366 days or 12 months
quarter	3 months
month	28-31 days; Jan., Mar., May, Jul., Aug. Oct., Dec. — 31 days; Apr., Jun., Sep., Nov. — 30 days; Feb. — 28 days for a common year and 29 days for a leap year
week	7 days
day	24 hours or 1,440 minutes or 86,400 seconds
hour	60 minutes or 3,600 seconds
minute	60 seconds
second	base unit
millisecond	10⁻³ second
microsecond	10⁻⁶ second
nanosecond	10⁻⁹ second
picosecond	10⁻¹² second

How do we measure time?

The calendar and the clock are two distinct systems of time quantification that are commonly employed today. These time measures are based on the sexagesimal numeral system, with the number 60 as its foundation. This system was developed in ancient Sumer around the third millennium B.C. and was adopted by the Babylonians.

We use the base 60 because the number 60 is the highest composite number with 12 coefficients. The highest composite number is a natural number that has the greatest ratio of the number of divisors to some positive degree of itself than any other number.

The mathematical advantage of the number 60 makes it convenient in practice. The number 60 has many divisors, which simplifies operations with fractions. We can divide one hour into 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, and 30-minute intervals without a remainder.

Invention of the second, minute, and 24-hour day

Egyptian culture was the first civilization to split the day into smaller halves. The first sundials split the time between dawn and sundown into 12 segments.

People could not use sundials after sundown, so determining the length of the night was more complicated. Egyptian astronomers spotted patterns in a group of stars, and used 12 of them to construct 12 segments of the night.

One argument for the genesis of the notion of a 24-hour day is the existence of these two 12-part splits of day and night. The Egyptians’ classifiers fluctuated according to the season, with summer hours lasting significantly longer than winter.

Later, between 147 and 127 B.C., a Greek astronomer named Hipparchus recommended dividing the day into 12 hours of daylight hours and 12 hours of darkness, depending on the days of the equinox.

Hipparchus also developed a model of longitude lines containing 360 degrees, which Claudius Ptolemy eventually divided into 360 degrees of latitude and longitude. He divided each degree into 60 parts, each divided into 60 smaller pieces, now called a minute and a second.

While various civilizations have changed alternative calendar systems over time, the Gregorian calendar is the most widely used globally. It was founded in 1582 by Pope Gregory XIII and is based primarily on the Julian calendar, a Roman solar calendar suggested by Julius Caesar in 45 B.C.

The Julian calendar was flawed, and the astronomical equinoxes and solstices were about 11 minutes ahead of it per year. The Gregorian calendar considerably reduced this disparity.

Early instruments for measuring time

Early clocks varied by culture and region, and were often intended to divide the day or night into distinct phases to control labor or religious routines. Oil lamps and candle clocks, for example, would show the flow of time from one event to the next instead of telling the time of day.

The water clock, also called the clepsydra, is often regarded as the most accurate timepiece of the ancient world. Clepsydra regulates water flow from or into the vessel, which is then analyzed to calculate the time duration.

Hourglasses, also known as sandglasses, emerged in the 14th century and served a role comparable to oil lamps and candle clocks. As the clock's precision increased, it began to be used to calibrate the hourglass to accurately record the length of time.

Christiaan Huygens invented the first pendulum mechanical clock in 1656. It was the first clock controlled by a device with a "natural" period of oscillation. Huygens refined his pendulum clock to have inaccuracies of less than 10 seconds every day.

Atomic clocks are the most accurate time-measuring tools available today. Even though there are various types of atomic clocks, cesium atomic clocks are the most popular and precise. They are calibrated by observing the emission periods of the cesium atoms. Atomic clocks use an electrical oscillator to measure time using cesium nuclear resonance.

Time Concepts

Aristotle

Throughout history, various scientists and philosophers have proposed several constructions of time. Aristotle (384–322 B.C.) described it as "various movements relative to before and after." This ancient Greek philosopher said that time quantifies changes that require some change or movement. He also believed that time was unlimited and constant, and that the cosmos had existed and would continue to exist indefinitely.

Newton

In his Philosophiae Naturalis Principia Mathematica, Newton addressed the notions of space and time as absolutes. He contended that absolute time exists and moves without regard to external causes, and he referred to this as "duration." Absolute time, according to Newton, can only be comprehended theoretically since it is indistinguishable.

Relative time is what people experience and is a value of "duration" based on moving objects like the sun and the moon. Newtonian time is a term that refers to Newton’s realist viewpoint.

Leibniz

Time, as per Leibniz, is nothing more than a notion, like space and numbers, that enables humans to assess and arrange experiences. It is how humans subjectively view and sequence the things, events, and experiences they have gathered during their existence. Unlike Newton, Leibniz believed that time is only important when there are entities with which it can interact.

Einstein

Unlike Newton, who believed that time flowed the same for all observers regardless of point of reference, Einstein presented the concept of spacetime as interconnected rather than separate concepts of space and time.

Einstein suggested that the speed of light, c, is a constant for all viewers in a vacuum, regardless of the speed of the light source. He stated that it connects distances recorded in space to distances recorded in time.

Ultimately, for viewers in different inertial conceptualizations (different relative velocities), both the structure of space and the characteristics of time change simultaneously because of the speed constant of light.

A typical example illustrating this involves a spacecraft traveling at close to the speed of light.

For an observer on another spacecraft traveling at a different speed, time on a spaceship traveling near light speed will go slower. It will theoretically stop if the spacecraft can reach the speed of light.

If an object moves faster in space, it will move slower in time; if it moves slower in space, it will move faster in time. This must happen for the speed of light to remain constant.

Numerous perceptions of time throughout human history show that scientists can debunk even the most perfect hypotheses formulated earlier.

Even after all the advances in quantum physics and other fields of knowledge, time remains an enigma. It may happen that Einstein’s universal constant of light will be invalidated after a while, and humanity will be able to travel back in time.