Five Time Calculations in One Tool
Time Between Two Times
Breaks to Deduct
Add Time to a Start Time
2h 35m, 2:35, 2.5h, 155 minutes, 2 hours 35 minutes 12 secondsSubtract Time from a Start Time
2h 30m, 1:15, 1.5h, 90 minutesHours, Minutes & Seconds to Decimal
Sum of Multiple Time Periods
2h 35m, 2:35, 2.5h, 155 minutesHow to Use the Time Calculator
1. Time Between Two Times
Use this mode to find how many hours and minutes between a start time and an end time. Enter the start time (e.g., 9:00 AM) and the end time (e.g., 5:30 PM). The calculator returns the gross duration in HH:MM:SS, decimal hours, and total minutes. To deduct a break (lunch, coffee, dinner), add a break entry below the time inputs.
2. Add Time to a Start Time
Use this mode to compute an end time from a start time and a duration. For example, "What time is it 2 hours 45 minutes after 9:30 AM?" Enter 9:30 AM as the start and 2h 45m as the duration. The result is 12:15 PM. If the sum crosses midnight, the calculator shows "next day" automatically.
3. Subtract Time from a Start Time
Use this mode to compute an earlier time from a start time and a duration. For example, "What time was it 1 hour 30 minutes before 5:00 PM?" Enter 5:00 PM as the start and 1h 30m as the duration. The result is 3:30 PM. If subtraction crosses midnight, the calculator shows "previous day" automatically.
4. Hours to Decimal Converter
Use this mode to convert hours, minutes, and seconds into a single decimal number. For example, 8 hours 30 minutes equals 8.50 decimal hours, which you can paste into Excel, Google Sheets, or an invoicing form. The output also includes total minutes (510) and total seconds (30,600) for spreadsheet formulas.
5. Sum of Periods
Use this mode to add up multiple time entries from a time tracker, billing log, or workout record. Separate each entry with a plus sign or a new line. Each entry can use any supported format (2h 35m, 2:35, 2.5h, 155 minutes).
Frequently Asked Questions
How do I calculate the time between two times?
Enter the start time and end time in the Time Between tab. The calculator converts both times to total seconds since midnight, computes the difference (handling overnight rollover automatically when end < start), and displays the result in 4 formats: HH:MM:SS, decimal hours, hours+minutes, total minutes. Optional: add a break period (e.g., 1h lunch) to deduct from the gross duration.
Does the calculator handle overnight times?
Yes. If the end time is earlier than the start time, the calculator assumes the duration crosses midnight and adds 24 hours. For example, 11:00 PM to 1:30 AM returns 2h 30m (not negative). A toggle labeled "End is later" lets you force non-overnight math when both times are on the same day.
How do I add hours and minutes to a time?
Use the Add Time tab. Enter the start time (e.g., 9:30 AM) and a duration (e.g., 2h 45m). The calculator adds the duration in seconds and displays the resulting end time in HH:MM:SS format. If the result crosses midnight, the time wraps around and a "next day" indicator is shown. Supports 12h (with AM/PM) and 24h input.
How do I convert hours and minutes to decimal?
Use the Hours to Decimal tab. Enter the duration in HH:MM:SS format (e.g., 8:30:00) or use the preset buttons (15 min = 0.25, 30 min = 0.5, 45 min = 0.75). The calculator returns the decimal hours (e.g., 8.5), total minutes (510), and total seconds (30600) so you can paste the exact value into a spreadsheet or invoicing form.
Can AI chatbots calculate time durations correctly?
AI text models are inconsistent with time math. They often confuse 12-hour and 24-hour formats (e.g., 13:00 vs 1 PM), mishandle overnight rollover (11 PM + 2h might return 11:00 PM instead of 1:00 AM), break deduction (subtract lunch from a 9-to-5 day), multi-period sum (2h 35m + 3h 45m + 1h 15m), hours-to-decimal rounding (8:30 = 8.5), and DST transitions. They also forget your previous calculation between prompts. This calculator uses standard time arithmetic with deterministic rounding, handles all edge cases, and persists your work in localStorage.
Can I sum multiple time periods?
Yes. Use the Sum of Periods tab. Type or paste a list of durations separated by plus signs (e.g., "2h 35m + 3h 45m + 1h 15m") or new lines. Each line is parsed, normalized to seconds, summed, and displayed as total duration. Useful for totaling time entries from a time tracker before invoicing or billing.
What input formats are accepted?
Five parsing patterns are supported for any duration input: "2h 35m" (suffix style), "2:35" (colon style), "2.5h" (decimal style), "155 minutes" (long form), and "2 hours 35 minutes 12 seconds" (longest form). Whitespace is flexible and case-insensitive. Hours, minutes, and seconds are all optional.
Does this tool store my times anywhere?
Only in your browser. All calculations run locally in JavaScript and your last input per mode is saved to localStorage so a page refresh keeps your work. Nothing is uploaded to a server. You can clear all stored data with the Reset button or by clearing browser storage for this site.
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