Add or Subtract Two Time Values
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.
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. The result will be the new time and date based on the subtracted or added period of time. To calculate the amount of time (days, hours, minutes, seconds) between times on two different dates, use the Time Duration Calculator.
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 −. "1d 2h 3m 4s + 4h 5s - 2030s" is an example of a valid expression.
A time calculator performs arithmetic on time values - adding or subtracting durations expressed in days, hours, minutes, and seconds. Unlike ordinary arithmetic, time does not use a base-10 system: 60 seconds make a minute, 60 minutes make an hour, 24 hours make a day, and 7 days make a week. This non-decimal structure makes mental time arithmetic error-prone and tedious, which is exactly what a time calculator eliminates.
This page offers three distinct time calculators, each suited to a different type of problem:
2d 4h 30m + 18h 45m - 3d 10s and evaluate the whole chain at once. Useful for combining several time intervals in a single calculation.Time arithmetic follows specific carry and borrow rules because each unit has a different base. Here is how to do it manually - and what the calculator does automatically.
Add each unit column independently (seconds, then minutes, then hours, then days), then carry any overflow to the next larger unit.
Example: Add 2 days 14 hours 47 minutes 38 seconds + 1 day 11 hours 25 minutes 50 seconds
Subtract each column right-to-left. If a column would go negative, borrow from the next larger unit.
Example: Subtract 3 hours 45 minutes 20 seconds from 5 hours 10 minutes 5 seconds
The time calculator handles these carry and borrow operations automatically, eliminating the most common source of errors in manual time arithmetic.
Understanding the relationships between time units is fundamental to working with time arithmetic. All conversions ultimately derive from a handful of exact definitions:
| Unit | Exact Equivalent | In Seconds |
|---|---|---|
| 1 second | Base SI unit | 1 s |
| 1 minute | 60 seconds | 60 s |
| 1 hour | 60 minutes = 3,600 seconds | 3,600 s |
| 1 day | 24 hours = 1,440 minutes = 86,400 seconds | 86,400 s |
| 1 week | 7 days = 168 hours = 604,800 seconds | 604,800 s |
| 1 month (avg.) | ~30.44 days = ~730.5 hours | ~2,629,746 s |
| 1 year (avg.) | 365.2422 days = 8,765.8 hours | ~31,556,926 s |
| 1 decade | ~3,652.4 days | ~315,569,260 s |
| 1 millisecond | 0.001 second | 0.001 s |
| 1 microsecond | 0.000001 second | 10⁻⁶ s |
| 1 nanosecond | 0.000000001 second | 10⁻⁹ s |
Note that a "month" and a "year" have no exact fixed length in seconds because calendar months vary from 28 to 31 days and years alternate between 365 and 366 (leap years). The values above are averages based on the Gregorian calendar cycle of 400 years.
The expression calculator (Calculator 3) is particularly useful when you need to chain multiple time additions and subtractions together in a single step. The syntax uses suffix letters to indicate the unit:
Units within a single term do not need to be in order and do not all need to be present. Only + and − are supported as operators. Examples of valid expressions:
8h 30m + 1h 45m + 2h 15m - adds three work blocks (result: 12h 30m)1d 2h 3m 4s + 4h 5s - 2030s - a mixed multi-step expression48h - 7h 23m 15s - subtract a duration from 48 hours90m + 45m - 30m - add and subtract minutes (result: 105m = 1h 45m)The result is displayed both in the compact Xd Yh Zm Ws format and as equivalent totals in each single unit (total hours, total minutes, total seconds), making it easy to convert directly to the unit you need.
Time addition and subtraction arise in dozens of everyday and professional contexts. Here are some of the most common use cases:
Project managers frequently need to add durations to determine end dates, or subtract elapsed time to find remaining time. If a task is estimated at 3 days 6 hours and the project started at 9:00 AM on Monday, the "Add or Subtract Time from a Date" calculator tells you the exact finish time and date - accounting for the transition across days.
Calculating total hours worked across a pay period requires adding multiple daily shift durations. For example, an employee who works 7h 45m on Monday, 8h 20m on Tuesday, 6h 50m on Wednesday, 9h 5m on Thursday, and 7h 30m on Friday has a total work week the calculator computes in seconds: 39h 30m. Compare that against the standard 40-hour week to determine overtime or undertime.
Multi-course meals and batch cooking require tracking multiple concurrent and sequential timers. Adding durations - "the roast needs 2h 45m, then rests for 20m, then slicing takes 10m" - gives the total kitchen time needed and the exact time to start each item.
Athletes and coaches add split times to find total race times, subtract elapsed times to compute remaining distance or pace, and use the expression calculator to total training hours for a week or month. A swimmer recording 5 training sessions of varying durations can sum them instantly to track weekly volume.
Adding a flight duration and layover to a departure time gives the arrival time - in the local time zone. Calculating total transit time across multiple legs (flight + ground transport + check-in wait) helps plan itineraries accurately. Subtracting a current time from a deadline reveals remaining time available.
Hospitals track medication administration intervals, surgery durations, patient monitoring periods, and shift changeover times - all requiring precise time arithmetic. A medication given at 6:20 AM every 8 hours should next be given at 2:20 PM and then 10:20 PM - calculations that are error-free when done with a time calculator but prone to mistakes when done mentally.
Video editors calculate total runtime by adding clip durations. Podcast producers total episode lengths for playlist planning. Broadcasters plan airtime blocks by adding segment durations and subtracting from the available time slot. The expression calculator is particularly handy here: enter all clip durations in one expression and get the total instantly.
Time is one of the most fundamental and yet most elusive concepts in human experience. Throughout history, philosophers, scientists, and mathematicians have wrestled with questions of what time actually is, whether it exists independently of the physical world, and how we can best measure it.
Aristotle was among the first to offer a systematic account of time, defining it as "the measure of motion according to before and after." In his view, time does not exist independently of events or change - without something happening, there would be nothing to count. This view linked time inseparably to physical processes in the world. Plato, by contrast, described time as a "moving image of eternity," suggesting that the regular cycles of celestial bodies were an imperfect copy of timeless mathematical forms.
In the 17th century, Isaac Newton introduced the concept of absolute time: a uniform, universal flow that exists independently of external things - a kind of cosmic clock ticking at the same rate everywhere in the universe. Gottfried Wilhelm Leibniz challenged this, arguing that time is relational rather than absolute - that is, time is nothing more than the order of events, and without events, there would be no time at all. This philosophical debate continued for centuries and was ultimately transformed by Einstein.
Albert Einstein's Special Theory of Relativity (1905) fundamentally overturned Newton's concept of absolute time. Einstein demonstrated that the passage of time is not universal - it depends on the relative velocity of the observer. An observer moving at high speed experiences time passing more slowly than a stationary observer, a phenomenon known as time dilation. His General Theory of Relativity further showed that gravity warps space and time, so time passes more slowly in stronger gravitational fields. Einstein unified space and time into a single four-dimensional fabric called spacetime, making the study of time inseparable from the geometry of the universe itself.
Time dilation is not merely theoretical - it has practical consequences. The GPS satellites orbiting Earth at high speed experience time running slightly slower than clocks on the ground (special relativistic effect), while the weaker gravity at altitude causes time to run slightly faster (general relativistic effect). GPS systems must account for both effects - a net gain of about 38 microseconds per day - to maintain the accuracy that navigation depends on.
The way we divide time into hours, minutes, and seconds derives from the ancient sexagesimal (base-60) numeral system developed by the Sumerians and Babylonians more than 4,000 years ago. Base 60 was favored because 60 is evenly divisible by 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, and 30 - making it ideal for fractions and astronomical calculations. This is why we still divide hours into 60 minutes and minutes into 60 seconds, even though almost all other modern measurement systems use base 10.
Today, the second is defined by atomic physics. Since 1967, the International System of Units (SI) has defined one second as exactly 9,192,631,770 cycles of the radiation emitted during the transition between two hyperfine levels of the ground state of a cesium-133 atom. Atomic clocks based on this definition are accurate to within about one second every 300 million years - far more precise than any celestial observation.
The ancient Egyptians divided the day into 24 parts - 12 daylight and 12 nighttime hours. Because day and night are different lengths across seasons, these "seasonal hours" varied in length throughout the year. Fixed, equal-length hours became possible only with mechanical clocks in the medieval period. The Greek astronomer Hipparchus (c. 147–127 BC) is credited with standardizing the 24 equal-hour day for astronomical purposes.
The word minute comes from the Latin pars minuta prima ("first small part"), meaning 1/60 of an hour. The second comes from pars minuta secunda ("second small part"), meaning 1/60 of a minute. Both terms reflect the sexagesimal division introduced by Babylonian astronomers and formalized by medieval European scholars working with their astronomical tables.
Sundials - Among the earliest known timekeeping devices, sundials track time by measuring the position of a shadow cast by a gnomon in sunlight. Ancient Egyptians used obelisks as large sundials as early as 3500 BC. The fundamental limitation: sundials work only in daylight and only in clear weather.
Water Clocks (Clepsydra) - Water clocks measured time by the regulated flow of water from one container to another, allowing timekeeping at night and indoors. They were developed around 1500 BC in Egypt and widely used in ancient Greece and Rome. Sophisticated versions included floats, gears, and indicating dials to improve accuracy.
Hourglasses - Sand glasses use the flow of sand through a narrow neck to measure fixed intervals. They became popular in medieval Europe from around the 14th century and were widely used at sea (for measuring the ship's speed using a knotted rope and log) and in kitchens and churches.
Mechanical Clocks - The first weight-driven mechanical clocks appeared in European towers around 1275–1325 AD. They used an escapement mechanism - a device that allows a wheel to advance by one tooth at each beat of the oscillator - to mark equal intervals of time. These early clocks were accurate to within about 15–60 minutes per day.
Pendulum Clocks - In 1656, Christiaan Huygens built the first practical pendulum clock, exploiting Galileo's earlier observation that a pendulum's period depends only on its length, not the amplitude of its swing. Pendulum clocks were accurate to within a few seconds per day - an order of magnitude better than prior mechanical clocks - and dominated precision timekeeping for nearly 300 years.
Quartz Clocks - In 1927, the first quartz crystal clock was developed at Bell Telephone Laboratories. Quartz clocks exploit the piezoelectric properties of quartz crystals, which oscillate at a precise frequency (typically 32,768 Hz) when an electric current is applied. Quartz clocks are accurate to about 1 second per year and form the basis of nearly all modern consumer clocks and watches.
Atomic Clocks - Modern atomic clocks, developed from the 1950s onward, use the extremely stable frequency of electromagnetic radiation emitted by atoms to measure time with nanosecond-level accuracy. The cesium fountain clock, the current standard, is accurate to about 1 second in 300 million years. Optical lattice clocks under development may achieve accuracy 100 times better still.
When adding time values where the minutes column exceeds 59, carry the overflow into hours: every 60 minutes becomes 1 hour. For example, 2h 45m + 1h 35m: minutes = 45 + 35 = 80 = 1h 20m carry; hours = 2 + 1 + 1 (carried) = 4 hours. Result: 4h 20m. The calculator performs this automatically - just enter the raw values and it handles all carrying.
This time calculator adds or subtracts time values or durations. The Time Duration Calculator finds the elapsed time between two specific clock times or dates. Use this calculator when you know a duration and want to find a result; use the duration calculator when you know two points in time and want to find the gap between them.
Yes. If the second time value is larger than the first in a subtraction, the result is negative and is displayed with a minus sign. For example, subtracting 5 hours from 3 hours gives −2 hours. This is useful when calculating whether a time budget has been exceeded.
The date calculator uses calendar-aware date arithmetic. If you add 45 days to January 20, it correctly rolls over into March (accounting for February's length and leap year status). If you add 730 days, it advances two years. The result always shows a valid calendar date, including the day of the week.
The expression calculator displays the result in four formats: the standard Xd Yh Zm Ws breakdown, and equivalents as total days (with decimal), total hours (with decimal), total minutes (with decimal), and total seconds. This is useful when you need the answer in a specific unit - for example, if you need total hours worked expressed as a decimal for payroll (e.g., 7.75 hours rather than 7h 45m).
Weeks are not included as a separate input because they convert exactly and unambiguously to days (1 week = 7 days), making a separate field redundant. To add 3 weeks, simply enter 21 in the Days field. The output also expresses results in days rather than weeks and days because day-level granularity is more universally useful across different applications.
The SI second is defined by the cesium-133 atomic transition and is accurate to about 1 second per 300 million years. For everyday time calculations involving hours, days, or weeks, this precision is essentially perfect. The atomic definition matters most for GPS navigation, telecommunications synchronization, financial trading timestamps, and scientific experiments - where errors at the nanosecond scale have real consequences. The timekeeping apps and devices most people use are synchronized to atomic standards via the Network Time Protocol (NTP), keeping them accurate to within milliseconds.