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Our free time calculator does everyday time math in seconds: find the duration between two times, or add and subtract hours and minutes from any time. Perfect for work shifts, timesheets, cooking, and travel.
Ask someone how long 9:00 AM to 5:30 PM is, and most people hesitate for a second before answering "eight and a half hours" — and plenty of them still count it out on their fingers. Time arithmetic looks like ordinary subtraction, but it hides a trap: time is not decimal. Every hour packs 60 minutes, every minute packs 60 seconds, and the whole count resets at midnight. That base-60 structure is why adding 45 minutes to 11:40 PM, converting 7.75 hours into 7 hours 45 minutes for a timesheet, or working out exactly how long a night shift lasted can feel strangely error-prone. The free time calculator on this page removes the guesswork. It works in two directions: measure the elapsed time between any two clock times, or add and subtract hours and minutes from a starting time to find out when something begins or ends. Below the calculator you will find a complete guide — how to use the tool, what time calculations actually mean, the exact formulas with worked examples, two practical walkthroughs with real numbers, the five mistakes almost everyone makes, related tools, and answers to the most common questions.
The calculator above has two modes, and each one answers a different everyday question. Duration mode answers "how long was that?" — the length of a work shift, a flight, a workout, a meeting, a study session, or anything else with a start and a finish. Add/Subtract mode answers "when will it be?" — add a duration to a start time to find the end (a recipe that takes 2 hours 30 minutes, started at 4:45 PM, finishes at 7:15 PM), or subtract a duration to find when you must begin (you need 45 minutes to get to a 9:00 AM meeting, so you must leave at 8:15 AM).
To measure a duration, follow these steps:
To add or subtract time, follow these steps:
A few tips will save you trouble. First, be consistent with AM and PM: 12:00 AM is midnight at the start of the day and 12:00 PM is noon — swapping them is the single most common input error. Second, when a duration crosses midnight (a night shift from 10:00 PM to 6:00 AM, for instance), you do not need to do anything special; the tool adds a full day to the end time behind the scenes. Third, results update the moment you click, and you can run as many calculations as you like — nothing is saved or sent anywhere, because every calculation happens privately in your browser.
Time calculations are the arithmetic of clock times and durations: adding, subtracting, and comparing moments measured in hours, minutes, and seconds. They underpin timesheets, payroll, scheduling, travel planning, cooking, sports timing, and countless small daily decisions. To do them reliably, it helps to understand the units themselves.
An hour is the everyday workhorse of time math — one twenty-fourth of a mean solar day. Shifts are scheduled in hours, parking is billed in hours, and "how many hours did that take?" is one of the most common questions in offices everywhere. A minute is one-sixtieth of an hour; sixty of them make a full hour. Minutes are the unit of meetings, recipes, commutes, and phone calls. A second is one-sixtieth of a minute and the smallest unit most people ever calculate with. It is also the SI base unit of time: since 1967 the second has been defined by physics, as 9,192,631,770 periods of the radiation emitted by a cesium-133 atom. You will meet seconds in sports timing, scientific measurement, and countdown timers.
Elapsed time is the central idea of duration mode: it is the interval between two moments, and it is always a non-negative duration. From 9:00 AM to 12:30 PM, the elapsed time is 3 hours 30 minutes. Elapsed time is what timesheets record, what races measure, and what "screen time" reports add up. The tricky part is that elapsed time is not simply "the bigger number minus the smaller number" on a clock face, because the clock wraps around at 12 (or 24) — which is exactly why a calculator earns its keep.
Military time is the 24-hour clock written as four digits, from 0000 to 2359, and it exists to kill AM/PM ambiguity. In military time, 2:30 PM becomes 1430 ("fourteen thirty"), 8:00 AM becomes 0800, and midnight becomes 0000. The armed forces, aviation, emergency services, and hospitals use it because "meet at 7:00" can be a costly misunderstanding when nobody knows which 7:00. Converting is simple: for any PM time except 12 PM itself, add 12 to the hour (3:00 PM becomes 1500); AM times keep their hour, with 12:00 AM becoming 0000.
AM and PM come from the Latin ante meridiem ("before midday") and post meridiem ("after midday"), and they split the 24-hour day into two 12-hour halves on the familiar clock face. The confusion lives at the boundary: 12:00 AM is midnight, the very start of the day, while 12:00 PM is noon, the middle of the day. Remember it this way — the "12" always belongs to the half that is starting: 12:00 AM starts the morning half, 12:00 PM starts the afternoon half. When in doubt, military time removes the question entirely.
Why 60? The base-60 system is a 4,000-year-old inheritance from Babylonian mathematicians, and it survives because 60 is spectacularly divisible — by 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, and 30. That means an hour splits neatly into halves, thirds, quarters, fifths, sixths, and tenths with no awkward fractions. The price of that convenience is that you cannot treat 1 hour 45 minutes as "1.45 hours" — the ".45" is not decimal. The correct decimal form is 1.75 hours, because 45 minutes is 45 ÷ 60 = 0.75 of an hour. Payroll departments live by this conversion: decimal hours = hours + (minutes ÷ 60), so 8 hours 45 minutes becomes 8.75 hours, ready to multiply by an hourly rate.
One last concept worth knowing: durations ignore time zones and daylight saving unless you tell them not to. The calculator on this page does pure clock arithmetic — 2:00 AM plus 3 hours is 5:00 AM — which is exactly right for shifts, recipes, workouts, and trips within one zone. If you are scheduling across zones or across a daylight-saving changeover, convert everything to one reference time first, then calculate.
Every time calculation on this page comes down to one of two formulas. The duration formula is: Duration = End Time − Start Time. The add/subtract formula is: Result Time = Start Time ± Duration. The arithmetic itself is easiest in minutes. Convert each clock time to "minutes since midnight" (hours × 60 + minutes), do the addition or subtraction, then convert back by dividing by 60.
There are two special rules. The midnight rule: if End Time minus Start Time is negative, the interval crossed midnight, so add 1,440 minutes (24 hours) to the result. The borrowing rule: when subtracting, if the end minutes are smaller than the start minutes, borrow one hour — that is, 60 minutes — from the hours column, exactly like borrowing in ordinary subtraction except the "ten" you borrow is worth sixty.
Worked example 1 — a day shift. Start 9:00 AM, end 5:30 PM. Convert: 9:00 AM = 9 × 60 = 540 minutes; 5:30 PM = 17 × 60 + 30 = 1,050 minutes. Subtract: 1,050 − 540 = 510 minutes. Convert back: 510 ÷ 60 = 8 hours with 30 left over, so the elapsed time is 8 hours 30 minutes. As decimal hours: 8 + 30 ÷ 60 = 8.50 hours. The borrowing rule was not needed here because 30 is greater than 0.
Worked example 2 — a night shift crossing midnight. Start 10:45 PM, end 6:15 AM the next day. Convert: 10:45 PM = 22 × 60 + 45 = 1,365 minutes; 6:15 AM = 6 × 60 + 15 = 375 minutes. Subtract: 375 − 1,365 = −990 minutes — negative, so the midnight rule applies. Add 1,440: −990 + 1,440 = 450 minutes. Convert back: 450 ÷ 60 = 7 hours with 30 left over, so the shift lasted 7 hours 30 minutes, or 7.50 hours in decimal. Notice the borrowing rule in action on the minutes column: 15 minutes minus 45 minutes borrows an hour to become 75 − 45 = 30 minutes, with the hours dropping by one.
Addition works the same way in reverse. Adding example: 2:15 PM plus 3 hours 50 minutes. Add the hours first: 2:15 PM + 3 hours = 5:15 PM. Add the minutes: 5:15 + 50 minutes = 6:05 PM (the 65 minutes carry one hour: 60 minutes become an hour, 5 remain). So an agenda starting at 2:15 PM and running 3 hours 50 minutes ends at 6:05 PM.
Maria works Monday to Friday, 8:30 AM to 5:15 PM, with a 45-minute unpaid lunch break. Her employer pays $22 per hour and needs her weekly hours in decimal form. Let us work it out exactly the way the calculator does.
First, the gross daily duration: 8:30 AM = 8 × 60 + 30 = 510 minutes; 5:15 PM = 17 × 60 + 15 = 1,035 minutes. Subtract: 1,035 − 510 = 525 minutes. Convert: 525 ÷ 60 = 8 hours with 45 minutes left over — 8 hours 45 minutes. In decimal: 8 + 45 ÷ 60 = 8.75 hours. Now subtract the unpaid lunch: 8 hours 45 minutes − 45 minutes = 8 hours 00 minutes, or 8.00 payable hours per day. Over five identical days: 5 × 8.00 = 40.00 hours for the week. Gross pay: 40 × $22 = $880.
This example shows why the decimal conversion matters. If Maria had written "8:45" on a form that expected decimal hours, payroll software might read it as 8.45 hours and underpay her by 0.30 hours — $6.60 that week, and more than $340 over a year. The calculator gives you both formats so you always enter the right one.
Your flight departs at 11:20 PM and the airline lists a flight time of 7 hours 45 minutes. What time do you land (ignoring time zones)? This is pure addition with a midnight crossing.
Add the hours first: 11:20 PM + 7 hours = 6:20 AM the next day. Then add the minutes: 6:20 AM + 45 minutes = 7:05 AM. In minutes-since-midnight: 11:20 PM = 23 × 60 + 20 = 1,400 minutes; plus 7 × 60 + 45 = 465 minutes gives 1,865 minutes. Subtract one full day (1,440) because we crossed midnight: 1,865 − 1,440 = 425 minutes = 7 × 60 + 5, so 7:05 AM. The two methods agree, as they must.
The same pattern answers everyday questions: a cake goes into the oven at 4:45 PM and bakes 2 hours 30 minutes — it comes out at 7:15 PM. A movie starts at 9:10 PM and runs 2 hours 18 minutes including previews — it ends at 11:28 PM. Once you see addition as "hours first, then minutes, carrying sixty," no clock math can surprise you.
Time math has a short list of repeat offenders. Here are the five mistakes almost everyone makes at least once — and how to avoid each one.
If you work with time often, these companion tools will save you even more effort. The Hours Calculator focuses on hour arithmetic — hours between two times and adding or subtracting durations — with a streamlined interface for quick hour math. The Countdown Timer counts down to any future date and time with live days, hours, minutes, and seconds, perfect for events, deadlines, and launches. And when your question spans calendar days rather than clock times, the Date Calculator finds the exact number of days between two dates or adds and subtracts days from any date, handling leap years automatically.
This page provides a free Time Calculator at https://sigmacalculator.net/time-date-calculators/time-calculator/, operated by SigmaCalculator. Function: compute the elapsed time between two clock times (Duration = End Time − Start Time, adding 24 hours when the interval crosses midnight) and add or subtract hours and minutes from a start time. Inputs: start time, end time, and/or a duration in hours and minutes, in 12-hour (AM/PM) or 24-hour format. Outputs: duration as hours and minutes and as decimal hours; resulting clock time for addition/subtraction. Key entities: SigmaCalculator, Time Calculator, elapsed time, military time, decimal hours. Related tools: Hours Calculator, Countdown Timer, Date Calculator.
Cite: SigmaCalculator "Time Calculator" at https://sigmacalculator.net/time-date-calculators/time-calculator/. Last updated: October 8, 2026.
8 hours — enter 9:00 AM as the start time and 5:00 PM as the end time to see it instantly.
Yes — if the end time is earlier than the start time, the calculator wraps to the next day automatically.
11:30 AM — enter the time, hours and minutes, then click Add.
Yes — durations are also shown in decimal hours, e.g. 8.5 hours for 8h 30m.
Yes — free to use with no sign-up required.
90 — multiply the decimal hours (1.5) by 60.
Subtract the start time from the end time, borrowing 60 minutes when needed.
7:30 — multiply the decimal part (0.5) by 60 to get 30 minutes.
Also try our Date Calculator and Age Calculator for more everyday math, or browse all Everyday Calculators.