Time Calculator
Basic Time Calculator
This calculator can be used to "add" or "subtract" two time values. Input fields can be left blank, which will be taken as 0 by default.
(Days1 × 86400 + Hours1 × 3600 + Minutes1 × 60 + Seconds1) ± (Days2 × 86400 + Hours2 × 3600 + Minutes2 × 60 + Seconds2) = Total Seconds
Example:
1 day, 2 hours, 30 minutes + 0 days, 3 hours, 45 minutes = 1 day, 6 hours, 15 minutes
Add or Subtract Time from a Date
Use this calculator to add or subtract time (days, hours, minutes, seconds) from a starting time and date.
New Date = Start Date ± (Days × 86400 + Hours × 3600 + Minutes × 60 + Seconds) in milliseconds
Example:
Today at 8:30 AM + 2 days, 5 hours = 2 days from today at 1:30 PM
Time Calculator in Expression
Use this calculator to add or subtract two or more time values in the form of an expression. An acceptable input has d, h, m, and s following each value, where d means days, h means hours, m means minutes, and s means seconds. The only acceptable operators are + and -.
Parse expression into components (Xd, Yh, Zm, Ws), convert each to seconds, then apply operations in order
Example:
"1d 2h 3m 4s + 4h 5s - 2030s" would calculate as:
1 day, 2 hours, 3 minutes, 4 seconds PLUS 4 hours, 5 seconds MINUS 2030 seconds
Understanding Time and How It’s Calculated
Just like regular numbers, time values can be added or subtracted. However, because time is divided into unique units, calculating it differs from standard decimal math. Here’s a breakdown of the most common time units and their definitions:
| Unit | Description |
|---|---|
| Millennium | 1,000 years |
| Century | 100 years |
| Decade | 10 years |
| Year (avg) | 365.242 days or 12 months |
| Common Year | 365 days |
| Leap Year | 366 days |
| Quarter | 3 months |
| Month | 28–31 days (varies by month) |
| 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 of time |
| Millisecond | 1/1,000 of a second |
| Microsecond | 1/1,000,000 of a second |
| Nanosecond | 1/1,000,000,000 of a second |
| Picosecond | 1/1,000,000,000,000 of a second |
How Time Has Been Understood Through History
Philosophers and scientists have explored the nature of time for centuries. Let’s take a look at how some of the most influential minds defined it:
Aristotle’s Concept of Time
The Greek philosopher Aristotle (384–322 BC) viewed time as a way to measure motion — a sequence of changes that occur in order. He believed time was continuous and infinite, existing alongside an eternal universe. Aristotle also questioned the very nature of time, suggesting it might not exist without motion to measure.
Newton vs. Leibniz: Absolute vs. Relative Time
In the 17th century, Isaac Newton proposed the idea of “absolute time” — a universal clock that ticks independently of everything else. According to Newton, this kind of time exists on its own and can be understood only through mathematics.
On the other hand, Gottfried Wilhelm Leibniz argued that time doesn’t exist as an independent entity. Instead, it’s a tool we use to organize events. Known as “relational time,” this theory holds that time only makes sense in relation to objects and changes in the world.
A famous debate between Newton’s supporter Samuel Clarke and Leibniz led to the “bucket argument,” where a spinning bucket of water formed a concave surface. Newton claimed this showed evidence of absolute space and time, while Leibniz disagreed.
Einstein’s Theory of Relativity
Albert Einstein revolutionized our understanding of time in the 20th century. Building on earlier ideas, he introduced the concept of spacetime — a fusion of space and time into a single, interconnected framework. Einstein demonstrated that time isn’t fixed; it can stretch or contract depending on an object’s speed or gravity, a phenomenon known as time dilation.
For instance, if a spaceship travels near the speed of light, time moves more slowly on that ship compared to a stationary observer. In extreme cases, time could almost stop. This is why astronauts traveling at high speeds would age more slowly than people on Earth.
Einstein’s general relativity also resolved Newton’s bucket argument. It explained that objects move along paths called geodesics in curved spacetime. When something rotates against this natural path, it experiences force — meaning motion and time are deeply linked to the geometry of space itself.
Modern Science Still Has Questions
Even with groundbreaking theories from Newton to Einstein, time remains a partially unsolved mystery. As physics evolves, we may one day uncover new insights that challenge today’s understanding — perhaps even finding a way to travel back in time.
How We Measure Time Today
Timekeeping today relies mainly on calendars and clocks. These systems are rooted in a numerical method called the sexagesimal system, which uses 60 as its base. Developed by the Sumerians and later adopted by the Babylonians, this system remains in use for measuring time, angles, and coordinates due to its flexibility in dividing units evenly.
For example, 60 minutes in an hour can be evenly divided by 30, 20, 15, 10, 5, and so on — making calculations easier.
Evolution of Time Units and the 24-Hour Day
Ancient Egyptians were among the first to divide the day using sundials. They split daylight into 12 parts and later used stars to divide nighttime into another 12, forming the basis for a 24-hour day.
However, early hours varied in length based on the season. It wasn’t until the Greek astronomer Hipparchus (circa 147 BC) that the idea of equal hours emerged — by using the equinox as a reference point. This led to the modern system of fixed 24-hour days.
Hipparchus also laid the groundwork for dividing circles and time into 360 degrees, which were split further into 60 minutes and 60 seconds. These units remain the global standard today.
The Gregorian Calendar and Its Origins
Our current calendar — the Gregorian calendar — was introduced in 1582 by Pope Gregory XIII. It refined the Julian calendar (established by Julius Caesar in 45 BC), which slightly misaligned with astronomical seasons. The Gregorian calendar fixed this, making it the most accurate and widely used calendar in the world today.
For more details on the history of the Gregorian Calendar, please refer to the date calculator.
Early Timekeeping Devices
Throughout history, different cultures used various tools to track time, often tied to work schedules or religious rituals. Some of the earliest examples include:
Sundials: Used to track daylight by the sun’s shadow
Water clocks (clepsydras): Measured time using the flow of water
Oil lamps and candle clocks: Marked the passage of time between events
Hourglasses: Eventually calibrated with mechanical clocks to track set intervals
In 1656, Christiaan Huygens invented the pendulum clock — one of the first accurate mechanical clocks. Later, atomic clocks became the gold standard in timekeeping. These rely on the vibrations of cesium atoms to measure time with incredible precision. In fact, the modern definition of a second is based on these atomic oscillations.
Conclusion: A Timeless Fascination
Time is an essential part of our lives, yet still filled with scientific mysteries. From ancient sundials to atomic clocks, humanity has always sought better ways to understand and measure it. As our understanding deepens, the nature of time may continue to surprise us — perhaps even leading to possibilities once thought impossible.