Time Addition Formulas — Every Time Calculation Formula in One Place

Q: What is the formula for adding hours and minutes?

Add hours to hours and minutes to minutes separately. If the minutes total is 60 or more, subtract 60 from the minutes and add 1 to the hours. For example, 2:45 + 1:30 = 3:75, then carry over to get 4:15.

Q: How do I convert decimal hours to minutes?

Multiply the decimal portion by 60 to get the minutes. For example, 2.75 hours: the whole part is 2 hours, and 0.75 × 60 = 45 minutes, so 2.75 hours = 2 hours 45 minutes.

Q: What is 0.75 hours in minutes?

0.75 hours equals 45 minutes. Multiply 0.75 by 60 to get 45. This is the same as three-quarters of an hour.

Q: How do you add time in Excel?

Enter times in cells formatted as time (e.g., 2:30:00), then use =SUM(A1:A10). Format the result cell as [h]:mm:ss (with square brackets around h) to show totals over 24 hours correctly.

Q: What is the ISO 8601 format for time duration?

ISO 8601 uses the format P[n]Y[n]M[n]DT[n]H[n]M[n]S. For example, PT2H30M means a duration of 2 hours and 30 minutes. The T separates date components from time components.

Q: How do you calculate total seconds from hours, minutes, and seconds?

Multiply hours by 3600, multiply minutes by 60, then add both to the seconds. Formula: Total Seconds = (Hours × 3600) + (Minutes × 60) + Seconds. For example, 1:30:15 = 3600 + 1800 + 15 = 5415 seconds.

Q: What is the formula for overtime pay?

Under the FLSA, overtime pay = Hours Over 40 × Hourly Rate × 1.5. For example, if an employee works 45 hours at $20/hour, overtime pay is 5 × $20 × 1.5 = $150. Some states have daily overtime thresholds as well.

Q: How do you handle carry-over in time addition?

When seconds total 60 or more, subtract 60 and carry 1 to minutes. When minutes total 60 or more, subtract 60 and carry 1 to hours. For example, 1:50:45 + 0:15:30: seconds 45+30=75, carry 1 to get 15 seconds. Minutes 50+15+1=66, carry 1 to get 6 minutes. Hours 1+0+1=2. Result: 2:06:15.

Q: How do you convert minutes to decimal hours for payroll?

Divide the minutes by 60 to get decimal hours. For example, 45 minutes / 60 = 0.75 hours. For payroll, round to two decimal places. This conversion is essential for accurate wage calculations.

Q: What is the difference between elapsed time and clock time?

Clock time refers to a specific point in time (e.g., 3:00 PM), while elapsed time is the duration between two points (e.g., 2 hours 15 minutes). Time addition formulas work with elapsed time durations, not clock times.

Verified formulas ISO 8601 compliant Updated Feb 2026

The formula for adding time is: add hours, minutes, and seconds in separate columns, then carry over any value of 60 or more to the next unit. For example, 2:45 + 1:30 becomes 3:75, and since 75 minutes ≥ 60, the result is 4:15. This base-60 carry-over rule applies to all time addition, subtraction, multiplication, and conversion calculations.

This page is a complete reference for every time math formula you need — from basic addition and subtraction to decimal conversions, ISO 8601 durations, and Excel-ready formulas. Whether you're building a timesheet calculator, processing payroll, or working through a homework problem, every formula below has been verified for correctness.

Operation	Formula	Example
Add time	Add columns, carry ≥ 60	2:45 + 1:30 = 4:15
Subtract time	Subtract columns, borrow when negative	5:10 − 1:20 = 3:50
To decimal hours	H + (M ÷ 60) + (S ÷ 3600)	3:45:00 = 3.75 hrs
Decimal to HH:MM	H = whole part; M = decimal × 60	2.5 hrs = 2:30
To total seconds	(H × 3600) + (M × 60) + S	1:15:22 = 4522 s
Multiply time	Convert to seconds × N, convert back	2:15 × 5 = 11:15
ISO 8601 duration	PT[H]H[M]M[S]S	PT2H30M = 2 h 30 min
Excel time sum	=SUM() with [h]:mm:ss format	=SUM(A1:A10)

What Is the Universal Formula for Adding Time?

Definition: Time addition is the process of combining two or more durations expressed in hours, minutes, and seconds into a single total duration, using modular (base-60) arithmetic to handle carry-overs between units.

Because minutes and seconds use a base-60 (sexagesimal) number system — a system first developed by the ancient Sumerians in the 3rd millennium BCE and later refined by the Babylonians — you cannot simply add time values the same way you add decimal numbers. Instead, time addition follows a convert → add → carry algorithm.

Key Takeaway: Add each column (seconds, minutes, hours) independently, then carry over any value of 60 or more to the next larger unit. This is the single most important rule in time arithmetic.

How Does the Convert-Add-Carry Algorithm Work?

To add two time values A (H₁:M₁:S₁) and B (H₂:M₂:S₂), follow these steps:

// Step 1: Add each column independently raw_seconds = S₁ + S₂ raw_minutes = M₁ + M₂ raw_hours = H₁ + H₂ // Step 2: Carry over seconds → minutes final_seconds = raw_seconds mod 60 carry_minutes = floor(raw_seconds / 60) // Step 3: Carry over minutes → hours final_minutes = (raw_minutes + carry_minutes) mod 60 carry_hours = floor((raw_minutes + carry_minutes) / 60) // Step 4: Final result final_hours = raw_hours + carry_hours Result = final_hours : final_minutes : final_seconds

Example: Add 2:45:50 and 1:30:25.

Seconds: 50 + 25 = 75 → 75 mod 60 = 15 seconds, carry 1
Minutes: 45 + 30 + 1 = 76 → 76 mod 60 = 16 minutes, carry 1
Hours: 2 + 1 + 1 = 4 hours

Result: 4:16:15

This same algorithm extends to adding three or more time values — simply sum each column across all entries before applying the carry-over logic. Try it instantly with our Time Addition Calculator.

What Is the Formula for Subtracting Time?

Time subtraction reverses the addition process. Instead of carrying over, you borrow from the next larger unit when a smaller unit goes negative. This is especially useful when calculating elapsed time between a start and end time.

// Subtract A − B where A = H₁:M₁:S₁ and B = H₂:M₂:S₂ // Step 1: Subtract seconds diff_seconds = S₁ − S₂ If diff_seconds < 0: diff_seconds = diff_seconds + 60 borrow_minutes = 1 Else: borrow_minutes = 0 // Step 2: Subtract minutes (including any borrow) diff_minutes = M₁ − M₂ − borrow_minutes If diff_minutes < 0: diff_minutes = diff_minutes + 60 borrow_hours = 1 Else: borrow_hours = 0 // Step 3: Subtract hours diff_hours = H₁ − H₂ − borrow_hours Result = diff_hours : diff_minutes : diff_seconds

Example: Subtract 1:20:45 from 5:10:30 (that is, 5:10:30 − 1:20:45).

Seconds: 30 − 45 = −15 → −15 + 60 = 45 seconds, borrow 1
Minutes: 10 − 20 − 1 = −11 → −11 + 60 = 49 minutes, borrow 1
Hours: 5 − 1 − 1 = 3 hours

Result: 3:49:45

Need to calculate time differences quickly? Use the Time Subtraction Calculator to verify your results.

How Do You Multiply and Divide Time by a Number?

Multiplying or dividing time durations by a scalar (a regular number) is common in payroll — for example, calculating weekly pay from a daily shift length, or splitting a total duration among team members. The trick is to convert the time to a single unit first, perform the operation, then convert back.

How Do You Multiply Time by a Number?

// Multiply time H:M:S by factor N // Step 1: Convert to total seconds total_seconds = (H × 3600) + (M × 60) + S // Step 2: Multiply result_seconds = total_seconds × N // Step 3: Convert back hours = floor(result_seconds / 3600) minutes = floor((result_seconds mod 3600) / 60) seconds = result_seconds mod 60 Result = hours : minutes : seconds

Example: A shift is 2:15:00 long. What is the total for a 5-day week?

Total seconds = (2 × 3600) + (15 × 60) + 0 = 7200 + 900 = 8100
8100 × 5 = 40500 seconds
40500 ÷ 3600 = 11 remainder 900 → 900 ÷ 60 = 15 remainder 0

Result: 11:15:00 (11 hours and 15 minutes per week)

How Do You Divide Time by a Number?

// Divide time H:M:S by divisor N // Step 1: Convert to total seconds total_seconds = (H × 3600) + (M × 60) + S // Step 2: Divide result_seconds = total_seconds / N // Step 3: Convert back (may produce fractional seconds) hours = floor(result_seconds / 3600) minutes = floor((result_seconds mod 3600) / 60) seconds = result_seconds mod 60 Result = hours : minutes : seconds

Example: Split 8:00:00 evenly among 3 people.

Total seconds = 8 × 3600 = 28800
28800 ÷ 3 = 9600 seconds
9600 ÷ 3600 = 2 remainder 2400 → 2400 ÷ 60 = 40 remainder 0

Result: 2:40:00 per person

How Do You Convert Between Time Formats?

Payroll systems, project management tools, and spreadsheets all use different time formats. Converting between them accurately is essential for calculating work hours. Below are the formulas for every common conversion.

How Do You Convert HH:MM:SS to Decimal Hours?

Decimal hours express time as a single number where the fractional part represents minutes and seconds as a fraction of an hour. This is the standard format for payroll calculations.

Decimal Hours = Hours + (Minutes / 60) + (Seconds / 3600)

Example: Convert 3:45:30 to decimal hours.

3 + (45 ÷ 60) + (30 ÷ 3600) = 3 + 0.75 + 0.00833 = 3.7583 hours

How Do You Convert Decimal Hours to HH:MM:SS?

// Convert D decimal hours to HH:MM:SS Hours = floor(D) Minutes = floor((D − Hours) × 60) Seconds = round(((D − Hours) × 60 − Minutes) × 60)

Example: Convert 5.3417 decimal hours to HH:MM:SS.

Hours = floor(5.3417) = 5
Minutes = floor(0.3417 × 60) = floor(20.502) = 20
Seconds = round(0.502 × 60) = round(30.12) = 30

Result: 5:20:30

How Do You Convert HH:MM:SS to Total Minutes?

Total Minutes = (Hours × 60) + Minutes + (Seconds / 60)

Example: Convert 2:30:45 to total minutes.
(2 × 60) + 30 + (45 ÷ 60) = 120 + 30 + 0.75 = 150.75 minutes

How Do You Convert HH:MM:SS to Total Seconds?

Total Seconds = (Hours × 3600) + (Minutes × 60) + Seconds

Example: Convert 1:15:22 to total seconds.
(1 × 3600) + (15 × 60) + 22 = 3600 + 900 + 22 = 4522 seconds

How Do You Convert Minutes to Hours and Minutes?

// Convert M total minutes to H hours and R minutes Hours = floor(M / 60) Minutes = M mod 60

Example: Convert 197 minutes to hours and minutes.
floor(197 ÷ 60) = 3 hours, 197 mod 60 = 17 minutes → 3:17

What Is the Complete Decimal Hours to Minutes Conversion Table?

This reference table shows every minute value from 1 to 59 with its decimal hours equivalent. This is essential for payroll processing where decimal hours are required for wage calculations. Use our Work Hours Calculator to convert automatically.

Minutes	Decimal	HH:MM
1	0.0167	0:01
2	0.0333	0:02
3	0.0500	0:03
4	0.0667	0:04
5	0.0833	0:05
6	0.1000	0:06
7	0.1167	0:07
8	0.1333	0:08
9	0.1500	0:09
10	0.1667	0:10
11	0.1833	0:11
12	0.2000	0:12
13	0.2167	0:13
14	0.2333	0:14
15	0.2500	0:15
16	0.2667	0:16
17	0.2833	0:17
18	0.3000	0:18
19	0.3167	0:19
20	0.3333	0:20
21	0.3500	0:21
22	0.3667	0:22
23	0.3833	0:23
24	0.4000	0:24
25	0.4167	0:25
26	0.4333	0:26
27	0.4500	0:27
28	0.4667	0:28
29	0.4833	0:29
30	0.5000	0:30

Minutes	Decimal	HH:MM
31	0.5167	0:31
32	0.5333	0:32
33	0.5500	0:33
34	0.5667	0:34
35	0.5833	0:35
36	0.6000	0:36
37	0.6167	0:37
38	0.6333	0:38
39	0.6500	0:39
40	0.6667	0:40
41	0.6833	0:41
42	0.7000	0:42
43	0.7167	0:43
44	0.7333	0:44
45	0.7500	0:45
46	0.7667	0:46
47	0.7833	0:47
48	0.8000	0:48
49	0.8167	0:49
50	0.8333	0:50
51	0.8500	0:51
52	0.8667	0:52
53	0.8833	0:53
54	0.9000	0:54
55	0.9167	0:55
56	0.9333	0:56
57	0.9500	0:57
58	0.9667	0:58
59	0.9833	0:59

Quick Reference: Common payroll values — 15 min = 0.25, 30 min = 0.50, 45 min = 0.75. For any minute value, divide by 60 and round to four decimal places.

What Is the ISO 8601 Duration Format?

ISO 8601 is the international standard for representing dates, times, and durations. Published by the International Organization for Standardization, it defines a machine-readable and unambiguous duration format used in APIs, databases, scheduling systems, and programming languages worldwide.

The duration format follows this pattern:

P[n]Y[n]M[n]DT[n]H[n]M[n]S Where: P = Period designator (always required at the start) Y = Years M = Months (before the T) D = Days T = Time designator (separates date from time components) H = Hours M = Minutes (after the T) S = Seconds

The P prefix is always required. The T separator is required when any time component (hours, minutes, seconds) is present. Zero-value components can be omitted.

What Are Common ISO 8601 Duration Examples?

Duration	ISO 8601	Explanation
1 hour 30 minutes	PT1H30M	Time only — no date component
2 hours	PT2H	Minutes and seconds omitted when zero
45 minutes	PT45M	Hours omitted when zero
90 seconds	PT90S	No need to convert to minutes
1 day 6 hours	P1DT6H	T separates day from hours
2 years 3 months	P2Y3M	Date-only duration — no T needed
1 year 2 months 10 days 5 hours 30 minutes	P1Y2M10DT5H30M	Full date and time duration
8 hours 15 minutes 30 seconds	PT8H15M30S	Typical workday representation

Developer Tip: Most programming languages parse ISO 8601 durations natively. In JavaScript, Luxon supports Duration.fromISO("PT2H30M"). In Python, use isodate.parse_duration("PT2H30M"). Check the NIST Time and Frequency Division for authoritative time measurement standards.

What Are the Excel Formulas for Time Calculations?

Microsoft Excel stores time as a fraction of a 24-hour day (e.g., 6 hours = 0.25). This decimal system makes arithmetic straightforward but introduces formatting quirks. Here are the most important formulas and techniques for working with time in Excel.

How Do You Create Time Values with TIME()?

=TIME(hours, minutes, seconds) Examples: =TIME(2, 30, 0) → returns 2:30:00 AM =TIME(0, 90, 0) → returns 1:30:00 AM (auto-converts) =TIME(14, 15, 45) → returns 2:15:45 PM

How Do You Add Time Values with SUM()?

The =SUM() function adds time values directly. However, Excel's default time format wraps around at 24 hours, which means 25 hours would display as 1:00:00 instead of 25:00:00.

// Standard addition =SUM(A1:A10) // CRITICAL: Format the result cell as [h]:mm:ss // The square brackets around h prevent the 24-hour wrap Format → Cells → Custom → [h]:mm:ss

Common Pitfall: Without the [h]:mm:ss format (square brackets around the h), Excel wraps hours at 24. If your employees' weekly totals exceed 24 hours — which they usually do — the result will be wrong. Always use [h]:mm:ss for summing work hours.

How Do You Format Time with TEXT()?

=TEXT(A1, "[h]:mm:ss") → "37:15:30" =TEXT(A1, "h:mm AM/PM") → "1:15 PM" =TEXT(A1, "[h]") → "37" (total hours only)

How Do You Convert Time to Decimal Hours in Excel?

// Multiply by 24 to get decimal hours =A1 * 24 // Example: cell A1 contains 2:30:00 =A1 * 24 → 2.5

How Do You Calculate Time Differences in Excel?

// Simple subtraction (end − start) =B1 - A1 // Handle overnight shifts (crossing midnight) =IF(B1 < A1, B1 + 1 - A1, B1 - A1) // Example: A1 = 10:00 PM, B1 = 6:00 AM =IF(B1 < A1, B1 + 1 - A1, B1 - A1) → 8:00:00

What Are Common Excel Time Pitfalls?

Watch out for these issues:

Excel cannot display negative time values by default. If a subtraction returns a negative result, the cell will show ########. Enable the "1904 date system" under File → Options → Advanced, or restructure your formula to always subtract the smaller value from the larger.

When importing CSV data, Excel may interpret time strings as text rather than time values. Use =TIMEVALUE("2:30:00") to convert text to a proper time value.

The TIME() function only accepts values up to 32767 for each argument. For very large time totals, build the value mathematically: =(hours/24) + (minutes/1440) + (seconds/86400).

Frequently Asked Questions

What is the formula for adding hours and minutes?

Add hours to hours and minutes to minutes separately. If the minutes total 60 or more, subtract 60 from the minutes and add 1 to the hours. For example, 2:45 + 1:30: hours = 2 + 1 = 3, minutes = 45 + 30 = 75. Since 75 ≥ 60, the result is 3 + 1 = 4 hours and 75 − 60 = 15 minutes, giving you 4:15.

How do I convert decimal hours to minutes?

Take the decimal portion (everything after the decimal point) and multiply it by 60. For example, 2.75 hours: the whole number is 2 hours, and 0.75 × 60 = 45 minutes. So 2.75 hours = 2 hours and 45 minutes. For payroll, you can refer to the full conversion table above.

What is 0.75 hours in minutes?

0.75 hours equals 45 minutes. Multiply 0.75 by 60 to get 45. This is the same as three-quarters of an hour, and it's one of the most commonly used decimal values in payroll — representing a 45-minute work period.

How do you add time in Excel?

Enter time values into cells formatted as time (e.g., 2:30:00), then use =SUM(A1:A10). The critical step is formatting the result cell as [h]:mm:ss with square brackets around the h. Without the brackets, Excel wraps totals at 24 hours, which means 30 hours would incorrectly display as 6:00:00. See the full Excel formulas section for more details.

What is the ISO 8601 format for time duration?

ISO 8601 represents durations using the format P[n]Y[n]M[n]DT[n]H[n]M[n]S. The P marks the start, and T separates date parts from time parts. For example, PT2H30M means 2 hours and 30 minutes. P1DT6H means 1 day and 6 hours. Zero-value components are simply omitted. Learn more in the ISO 8601 section above.

How do you calculate total seconds from hours, minutes, and seconds?

Multiply hours by 3600, multiply minutes by 60, then add both results to the seconds. The formula is: Total Seconds = (Hours × 3600) + (Minutes × 60) + Seconds. For example, 1:30:15 converts to (1 × 3600) + (30 × 60) + 15 = 3600 + 1800 + 15 = 5415 total seconds.

What is the formula for overtime pay?

Under the Fair Labor Standards Act (FLSA), overtime pay is calculated as: Overtime Pay = Hours Over 40 × Hourly Rate × 1.5. For example, if an employee works 47 hours at $22/hour, their overtime pay is 7 × $22 × 1.5 = $231. Note that some states (such as California) also require daily overtime for hours exceeding 8 per day. Use our Overtime Calculator for quick calculations.

How do you handle carry-over in time addition?

When seconds total 60 or more, subtract 60 and carry 1 to the minutes column. When minutes total 60 or more, subtract 60 and carry 1 to the hours column. For example, adding 1:50:45 + 0:15:30: seconds = 45 + 30 = 75, carry 1 to get 15 seconds; minutes = 50 + 15 + 1 = 66, carry 1 to get 6 minutes; hours = 1 + 0 + 1 = 2. Final result: 2:06:15.

How do you convert minutes to decimal hours for payroll?

Divide the minutes by 60 to get decimal hours. For example, 45 minutes ÷ 60 = 0.75 hours. For payroll, round to two decimal places. A full 8-hour-and-45-minute day is 8 + (45 ÷ 60) = 8.75 decimal hours. This is the format most payroll systems expect for calculating gross wages.

What is the difference between elapsed time and clock time?

Clock time refers to a specific point in time (e.g., 3:00 PM), while elapsed time is the duration between two points (e.g., 2 hours 15 minutes). The time addition formulas on this page work with elapsed time durations — they represent "how long" something took, not "when" it happened. Use our Elapsed Time Calculator to find the duration between two clock times.

How do you add hours and minutes without a calculator?

Write the times in columns, aligning hours, minutes, and seconds. Add each column from right to left. If seconds total 60 or more, write the remainder and carry 1 to minutes. Repeat for minutes. For example, 1:45 + 2:30: minutes = 45 + 30 = 75, write 15 and carry 1; hours = 1 + 2 + 1 = 4. Answer: 4:15.

Why does time use base 60 instead of base 10?

The base-60 system was first developed by the ancient Sumerians in the 3rd millennium BCE, then refined by the Babylonians. It was adopted for timekeeping because 60 is highly divisible — it divides evenly by 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, and 30 — making it practical for splitting hours into halves, thirds, quarters, and fifths without fractions.

What is 2 hours and 45 minutes in decimal?

2 hours and 45 minutes equals 2.75 decimal hours. Divide the minutes by 60: 45 ÷ 60 = 0.75, then add to the hours: 2 + 0.75 = 2.75. This is the value you would enter into payroll software or a timesheet. See the complete conversion table for every minute value from 1 to 59.

How do I calculate work hours from clock-in and clock-out times?

Subtract the clock-in time from the clock-out time using the time subtraction formula, then deduct any unpaid break time. For example, clock in at 8:30 AM, clock out at 5:15 PM: 17:15 − 8:30 = 8:45, minus a 0:30 lunch break = 8:15 of work, or 8.25 decimal hours. Use our Work Hours Calculator for instant results.

Other Free Time Calculators

Time Addition Calculator

Add multiple time values in hours, minutes, and seconds with automatic carry-over.

Work Hours Calculator

Calculate total work hours, breaks, and overtime from start and end times.

Timesheet Calculator

Enter daily clock-in and clock-out times to compute weekly totals and gross pay.

Time Subtraction Calculator

Subtract one time duration from another with automatic borrowing.

Elapsed Time Calculator

Find the exact duration between two clock times, including across midnight.

Overtime Calculator

Calculate overtime pay with federal and state-specific rates and thresholds.

Disclaimer: The formulas and information on this page are provided for educational and reference purposes. While all calculations have been verified for accuracy, they should not be used as a substitute for professional payroll, accounting, or legal advice. Overtime rules vary by state and employment classification under the FLSA (29 CFR § 785.48). Consult a qualified professional for your specific situation.

Last updated: February 8, 2026