Use this add time / subtract time calculator to easily add or subtract time to any date, add/subtract hours, minutes or seconds to a particular time. Versatile online time adder to see what time will it be in X hours, minutes, days, etc.

Quick navigation:

- How to do time calculations
- What time will it be in X hours or minutes
- Examples of addition and subtraction of time intervals
- Commonly used time units
- History of time keeping and time calculation
- The importance of time measurement

## How to do time calculations

To add and subtract time with the time calculator you need to know the initial time you want to start with. For example 15 Sept. 2012, 12:00 (British) or Sept. 15, 2012, 11am (American). The clock calculator allows you to add or to subtract from that time, calculating the final result to the second, if needed.

When calculating time it is important to be aware that there are exceptions to some of the commonly accepted assertions. For example, a year is accepted to be 365 days but sometimes it is 366; a month is around four weeks but not precisely 28 days, etc. So, if relevant to your case, be sure to acknowledge this. This online time calculator, however, will be precise in its results regardless of whether you are working with a leap year or not, for example. Simply be sure to provide the correct data in the forms above.

If performing time addition or time subtraction by hand, a good approach is to first convert the input time interval into a convenient unit with a fixed number of seconds (see the table), and then to start with the greatest time unit that would be altered and move down towards the smallest one. This is most important when it comes to addition or subtraction of months, years, or decades.

## What time will it be in X hours or minutes

One of the most common applications of a time calculator is to determine what time will be a given number of hours into the future. Questions like "What time will it be in 20 minutes?" or "What time will it be in 20 hours?" can easily be answered by time algebra.

To get the answer while using our tool above, simply load the page (or reload if it is already open) so the "Initial Date & Time" fields show your current date and time. Then, enter the number of hours or minutes in the respective field and press "Calculate". For example, enter 10 in the "Hours" field to see what time it will be in 10 hours, or enter "10" in the "Minutes" field to see what time it will be in 10 minutes.

## Examples of addition and subtraction of time intervals

** Example 1:** You might wish to cook a meal which needs to be in the oven for 6.30 hours. Let's say right now it is 11:20 and you want to find out when to set the oven timer to. You need to enter "11:20" in the "Time" box and then using the "add time" function you will enter "6" in the "hours" box and "30" in the "minutes" box. By hitting the "calculate" button you will be shown the result in the bottom, which in this case is 17:50, or 5:50 pm.

** Example 2:** If your doctor asks you to go for a check-up in 18 days, you might want to set a reminder. To estimate when your check-up is due, first enter the current date, e.g. 20.05.2018 or May 20

^{th}, 2018. Then enter how many days you wish to add, in this case it is 18, and click "calculate" above. The time adder will do the rest.

## Commonly used time units

Understanding all time units is important for accurate time addition / subtraction. Converting all times, including the interval to add or subtract to seconds and then working with timestampts is often the preferred way of going about it.

Time unit | Equals | In seconds |
---|---|---|

Millennium / kiloyear | 1000 years | it depends |

Century | 100 years | it depends |

Decade | 10 years | it depends |

Year | 365 or 366 days* ~52 weeks | ~31,557,600 seconds |

Month | ~4 weeks 28-31 days | 2,419,200 - 2,678,400 seconds |

Week | 7 days 168 hours 10,080 min | 604,800 seconds |

Day | 24 hours 1,440 min | 86,400 seconds |

Hour | 60 minutes | 3,600 seconds |

Minute | 60 seconds | 60 seconds |

Second | base unit** | - |

* Every four years there is a "leap year" with 366 days due to February having one more day. 2016 and 2020 are such years. This also affects the number of hours, minutes, and seconds in a year.

** The second is the SI (The International System of Units) base unit. It can be written as sec or s. From it all other units are derived.

## History of time keeping and time calculation

Understanding time keeping can help you better understand time calculations and their complexities. The system by which we keep time is called **Sexagesimal**and goes as far back as 2000 b.c. It is used for measuring time, angles, and geographic coordinates. It has **sixty as its base**: 60 minutes in an hour, 60 seconds in a minute. It is suggested that the reasons for the origins of the system are based on the fact that people are able to count to twelve on one hand (using the thumb). However, the civilizations first to invent this used either a 60-based or a 12-based system (duodecimal).

Egyptians are thought to be the first to invent the sundial and used it to divide the day into **twelve parts**. This was probably due to the number of lunar cycles or because of the counting technique using the thumb. At this point people did not think of the night as a continuation of the day, but rather the opposite of it, thus the number 12 instead of 24. It is unknown where the number 60 came from, however, it is possible that this was due to it being the smallest number divisible by the first six counting numbers (1-6) as well as by 10, 12, 15, 20, and 30.

It should be noted that the public did not think about minutes and seconds until much later. This happened only when the **mechanical clocks** were created to display minutes at about the end of the 16^{th} century. So until then, time calculations would mainly concern days, weeks, months, and years.

Until not so long ago seconds were defined **based on astronomical events**. However, in 1967 it was redefined as the duration of 9,192,631,770 energy transitions of the cesium atom. This led to **atomic timekeeping**, which is accurate to 1 second over 20 million years, and Coordinated Universal Time (UTC), allowing for much more precise time calculations such as those performed by our software.

## The importance of time measurement

The ability to measure time precisely is one of the greatest human inventions! Precise time measurement as well as addition and subtraction of time intervals are crucial to a variety of economic activities around the world and the importance of precise time-keeping cannot be underestimated.

Applications dependent upon it include communication systems where networks need to be synchronised precisely, power grids, and finances, where timestamps accompany each transaction you make, and GPS - the Global Positioning System satellite navigation systems, which rely on time stamped signals to provide us with a precise location of a GPS receiver. By measuring the signal from four (or more) satellites, the user's position can be determined. The time measurement in GPS has to be incredibly accurate since light travels 30 centimetres in one nanosecond so even a tiny error in the time measurement could put you off course by many meters or even miles.

Therefore time is used for the precision navigation of ships, airplanes, and family cars, but what GPS sattelites also do is broadcast timing signals from their atomic clocks. These are then used by the abovementioned industries. For example, wireless telephone and data networks use GPS atomic time and in-built time calculators to keep their base stations in perfect synchronization which allows for more efficient sharing of the limited radio spectrum by mobile phones. Similarly, digital broadcast radios make use of GPS time to ensure the bits from all radio stations arrive at receivers in lockstep, meaning listeners can tune between stations very quickly.

Another example is the U.S. Federal Aviation Administration (FAA), which uses GPS to synchronize reporting of hazardous weather from its 45 Terminal Doppler Weather Radars covering the United States. This is just one scenario in which distributed networks of instruments must work together to precisely measure common events. Such networks require timing sources that can guarantee time accuracy at several points.

In light of the above, while our **time calculator** is just a small tool that can help you in daily tasks that require time management, it is also a symbol of the progress of humanity. Use it to easily add or subtract time when needed.

#### References

1 Lombardi, M. (n.d.) "Why is a minute divided into 60 seconds, an hour into 60 minutes, yet there are only 24 hours in a day." [online] Available at: https://www.scientificamerican.com/article/experts-time-division-days-hours-minutes/

2 "Units of Measurement". [online] Available at: http://www.exactlywhatistime.com/measurement-of-time/units-of-measurement/

3 "GPS Timing" [online] Available at: https://www.gps.gov/applications/timing/

## FAQs

### How do you calculate time easily? ›

**How to Calculate the Elapsed Time**

- Count the number of minutes from the first time to the hour that comes after it.
- Count on in hours until the hour immediately before the final time.
- Count the number of minutes from this hour until the final time.
- Add the hours and minutes to find a total.

**Do you add or subtract clock times? ›**

Adding time to clock

e.g., What time will it be in 30 minutes? **Add the hours and the minutes separately**. If the minutes are >= 60, subtract 60 from the minutes and add 1 to hours. If the hours are >= 24, set hours to "hours mod 24".

**How do you add hours and minutes and seconds? ›**

**Adding Hours, Minutes, and Seconds**

- Subtract 60 from the number of minutes.
- Increase the number of hours by one.
- If the number of minutes is still 60 or more, repeat the same process.

**What is the time formula formula? ›**

Ans. The Formula of time basically means the time which is or will be taken by any object or a thing a cover or completes a particular distance at a given speed the formula of time is: **Time = distance/ speed**.

**What is the formula for time subtraction? ›**

For example, calculate the difference between 6:20 and 9:00. Step II: Subtract the minutes: 60 – 20 = 40 . Step III: Subtract the hours: 8 – 6 = 2 . So, the difference between the given time is 2 hours and 40 minutes.

**Do you do times or addition first? ›**

Returning to the above example, the correct answer would be the first answer as it follows the rules of BODMAS: division can be done before multiplication and must be done before addition, and **multiplication comes before addition**.

**What is 30 minutes from 11 45? ›**

30 minutes after 11:45 am is **12:15 pm**.

**How do you calculate hours and pay? ›**

First, **determine the total number of hours worked by multiplying the hours per week by the number of weeks in a year (52).** **Next, divide this number from the annual salary**. For example, if an employee has a salary of $50,000 and works 40 hours per week, the hourly rate is $50,000/2,080 (40 x 52) = $24.04.

**When should kids add and subtract? ›**

**Between the ages of 5 and 7**, your child will start working on simple addition and subtraction problems and basic fractions.

**What is the solution for time math? ›**

To solve for time, **divide the distance traveled by the rate**. For example, if Cole drives his car 45 km per hour and travels a total of 225 km, then he traveled for 225/45 = 5 hours.

### How do you teach time difference? ›

In this strategy, students first draw a number line with the starting time on the far left. Then, they will move up to the end time by first moving up to the nearest hour of the end time or moving up however many minutes it takes to get to the nearest hour.

**What is 2 hours 15 minutes 30 seconds by 11? ›**

Answer. Therefore, 9030 seconds by 11 = **820.90909091 seconds**. Hope it helps, Mark me as brainliest.

**What is used to calculate time? ›**

**Digital Clock or the 24-hour clock**

Generally, we use the 12-hour clock to measure time.

**What is the rule for addition and subtraction? ›**

The rules to add and subtract numbers are given below: **Addition of two positive numbers is always positive**. Addition of two negative numbers is always negative. Subtraction of two positive numbers can be either positive or negative.

**Why do we use times before addition? ›**

By remembering that multiplication is repeated addition, we discovered it makes more sense that we multiply before adding because **multiplying is repeated addition**.

**What are the four rules of maths? ›**

The four basic Mathematical rules are **addition, subtraction, multiplication, and division**.

**What time is it 15 minutes before 9? ›**

**Quarter to 9** is the same as 15 minutes to 9. Meghan fell asleep when it was 15 minutes before 9 o'clock.

**What time is 15 minutes before 2? ›**

15 minutes before any hour is called Quarter to hour. So, 15 minutes before 2:00 means **Quarter to 2**.

**How do you calculate 3 hours and 45 minutes? ›**

Therefore, 3 hours 45 minutes =**3×60+45=180+45=225 minutes**.

**How to calculate 45 minutes on calculator? ›**

45 minutes is **45 minutes * (60 seconds / 1 minute)** = 45 * 60 seconds = 2700 seconds.

### How many hours is 7 30am 4 00pm? ›

How many hours from 7:30 am to 4:30 pm? **9 hours**.

**How do you add hours in a day? ›**

**Find 7 More Hours in a Day**

- Handle things once (saves 15 to 20 minutes). ...
- Don't listen to the news first thing in the morning (30 minutes). ...
- Make good use of waiting time (30 minutes). ...
- Think "half-time" (30 minutes). ...
- Be decisive and move on (up to 60 minutes). ...
- Lighten up on your cleaning standards (30 to 45 minutes).

**Can you add and subtract at the same time? ›**

**Addition and subtraction also work together**. You can do subtraction first, or you can do addition first. They are part of the same step, however, they can only be done after items in parentheses, exponents, and any multiplication and division.

**How do you add time difference? ›**

If the start minutes are higher than the end minutes, **subtract one hour from the end hours and add 60 minutes to the end minutes**. Subtract the start time minutes from the end minutes. Perform the same subtraction operation for the hours. Finally, combine the hours and minutes results to get the answer.

**How do you calculate hours and minutes? ›**

If you want to convert hours and minutes to just hours, **divide the minutes by 60 and add the unchanged hours**. If you want the result in minutes, multiply hours by 60 and add the unchanged minutes.

**How to do addition and subtraction of time in Excel? ›**

**In other words, you want the elapsed time or the difference between two times.**

- In cell B2 type the start time, enter a space, and then type “a” for AM or “p” for PM, and press Enter. ...
- In cell D2, subtract the end time from the start time by typing the formula: =C2-B2, and then pressing Enter.

**Why is it easier to add then subtract? ›**

By analyzing children's accuracy and reaction time, it was concluded, in light of Piaget's theory, that subtraction is harder than addition because **children deduce differences from their knowledge of sums**.

**What is the rule for adding and subtracting? ›**

The rules to add and subtract numbers are given below: **Addition of two positive numbers is always positive**. Addition of two negative numbers is always negative. Subtraction of two positive numbers can be either positive or negative. Subtraction of two negative numbers can be either positive or negative.

**How do you calculate difference in hours? ›**

**To calculate the number of hours between two times:**

- Convert both times to a 24-hour time format.
- Subtract the starting time from the ending time.
- Do you have any seconds or minutes after the subtraction? If so: ...
- Voila! You have calculated the hours between times.

**How do I add 15 minutes to a time in Excel? ›**

Using the TIME Function to Add Minutes to Time in Excel

To add a specific number of minutes to a time value using the TIME function, you can use the following formula: **"=A1+TIME(0,15,0)"** (where "A1" is the original time value, and "TIME(0,15,0)" adds 15 minutes to the time value).

### How do you subtract 30 minutes from a time in Excel? ›

If you want to subtract minutes instead of hours, you can simply **enter the number of minutes in the cells youre subtracting**. For example, if you want to subtract 30 minutes from 1:00 PM, you would enter "30" in cell A2 instead of "5:00."