# Time calculator: add and subtract hours and minutes

> Add and subtract hours, minutes and seconds from a list of durations, with the total as H:MM:SS, decimal hours, minutes and seconds.

Versión interactiva: https://www.calcopenly.com/es/datetime/time-duration-calculator
Tema: Calculadoras de fecha y hora

Each line is converted to seconds (3,600 × hours + 60 × minutes + seconds), lines that start with a minus sign are subtracted, and the sum is turned back into hours, minutes and seconds. Entries can be written as H:MM:SS, H:MM, 2h 15m, 90 min or 1.5 h. The total is a duration, not a time of day, so 23:59:59 plus one second gives 24:00:00 rather than wrapping to midnight.

Typical uses are adding up timesheet entries, video clip lengths, lap splits and flight legs. The default list, 1:45:30 plus 2:20:15 minus 0:30:00, totals 3:35:45, which is 3.5958 decimal hours or 215.75 minutes.

Decimal hours are the total seconds divided by 3,600, the form payroll and invoicing systems usually ask for: 7 hours 45 minutes is 7.75 hours. To find the time between a start and an end time of day, use the hours calculator instead.

## Datos

- **Durations, one per line**: H:MM:SS or H:MM, or 2h 15m, 90 min, 1.5 h. Start a line with − to subtract it.

## Resultados

- Total — resultado principal
- Total as H:MM:SS
- Decimal hours (h)
- Total minutes (min)
- Total seconds (s)

## Fórmula

$$
T = \sum_i \pm (3600\,h_i + 60\,m_i + s_i)\ \text{s},\qquad \text{decimal hours} = T / 3600
$$

## Ejemplos resueltos

### Two additions and a subtraction

- Durations, one per line: 1:45:30 / 2:20:15 / - 0:30:00
- **Total: 3 h 35 min 45 s**
- **Total as H:MM:SS: 3:35:45**
- **Decimal hours: 3.5958 h**
- Fuente de comprobación: Python fractions: (6330 + 8415 − 1800) s = 12945 s = 3 h 35 min 45 s; 12945/3600 = 3.5958333…

### Carrying past 24 hours

- Durations, one per line: 23:59:59 / 0:00:01
- **Total: 1 d**
- **Total as H:MM:SS: 24:00:00**
- **Decimal hours: 24 h**
- Fuente de comprobación: 86399 + 1 = 86400 s by hand

### A negative total

- Durations, one per line: 1:00 / - 2:30
- **Total: −1 h 30 min**
- **Total as H:MM:SS: −1:30:00**
- **Decimal hours: -1.5 h**
- Fuente de comprobación: 3600 − 9000 = −5400 s by hand

### Mixed notations

- Durations, one per line: 90 min / 1.5 h / 45 s
- **Total: 3 h 45 s**
- **Total minutes: 180.75 min**
- Fuente de comprobación: 5400 + 5400 + 45 = 10845 s; 10845 / 60 = 180.75 by hand

## Preguntas

### How do I add hours and minutes together?

Add the hours and the minutes separately, then carry every 60 minutes into an hour. 1:45 plus 2:20 gives 3 hours and 65 minutes, and 65 minutes is 1 hour 5 minutes, so the total is 4:05. Seconds carry into minutes the same way. Typing each duration on its own line here does the carrying for you.

### How do I convert minutes to decimal hours?

Divide the minutes by 60. 15 minutes is 0.25 hours, 45 minutes is 0.75 hours, so 7 hours 45 minutes is 7.75 hours, and 3:35:45 is 12,945 ÷ 3,600 = 3.5958 hours. When a timesheet rounds to two decimals, each 0.01 hour is 36 seconds, so 3.5958 is entered as 3.60.

### How do I convert decimal hours back to hours and minutes?

Keep the whole hours and multiply the decimal part by 60 to get minutes. 1.5 hours is 1 hour 30 minutes, 3.6 hours is 3 hours 36 minutes and 0.1 hours is 6 minutes. Type an entry such as 3.6 h on a line here to see it shown as 3:36:00.

### How do I subtract one time duration from another?

Start the line with a minus sign. If the minutes to take away are larger, borrow 60 minutes from the hours: 2:10 minus 0:45 becomes 1:70 minus 0:45, which is 1:25. The total can go below zero; 1:00 minus 2:30 gives −1:30:00, an hour and a half short.

### How do I add times in Excel without the total resetting at 24 hours?

Excel stores a time as a fraction of a day, so a plain h:mm format wraps after 24 hours and 25 hours shows as 1:00. Format the total cell with the custom format [h]:mm:ss and the square brackets let hours run past 24. To get decimal hours in Excel, multiply the time by 24.

### ¿Qué precisión tiene «Time calculator: add and subtract hours and minutes»?

La precisión depende de tus datos y de los supuestos del método. El cálculo decimal usa 50 cifras significativas, pero las estimaciones, los métodos numéricos y los datos de origen pueden ser menos precisos; el redondeo mostrado no elimina esos límites. Ejemplos resueltos comprobados con fuentes independientes: 4. Por ejemplo, «Two additions and a subtraction» se comprueba con Python fractions: (6330 + 8415 − 1800) s = 12945 s = 3 h 35 min 45 s; 12945/3600 = 3.5958333….

### ¿De dónde procede el método?

ISO 8601-1:2019 — durations and the extended time format hh:mm:ss; BIPM, The International System of Units (SI), 9th ed. — minute and hour as non-SI units accepted for use with the SI.

## Fuentes

- ISO 8601-1:2019 — durations and the extended time format hh:mm:ss
- [BIPM, The International System of Units (SI), 9th ed. — minute and hour as non-SI units accepted for use with the SI](https://www.bipm.org/en/publications/si-brochure)