About

Time is the most critical resource in engineering, finance, and project management, yet standard tools fail to account for the complexities of the human calendar. This Time Duration Calculator is engineered for professionals who need more than just "days between dates." It addresses the specific problem of Billable Work Time - calculating the exact number of working hours between two timestamps, strictly adhering to custom business schedules (e.g., 09:00 to 17:00) while excluding weekends and non-working intervals.

Precision is paramount. A standard calculation of "2 days" implies 48 hours, but in a business context, it may only represent 16 billable hours. Errors here lead to payroll discrepancies, project slippage, and contract disputes. This tool utilizes Unix Epoch millisecond precision to handle complex temporal arithmetic, including leap years, variable month lengths, and boundary crossings (midnight rollovers). It offers three distinct operational modes: Absolute Precision Difference, Business Work-Hour Calculation, and Cumulative Time Chaining.

Formulas

For Absolute Duration, the calculation is a straightforward linear subtraction of timestamps T in milliseconds:

T_diff = | T_end − T_start |

For Work Hours (Billable Time), the logic is significantly more complex. We define a work interval W as the intersection of the calendar day D and the work shift range [h_start, h_end]. The total work duration T_work is the sum of valid intervals:

T_work = end∑d=start Valid(d) × Overlap(d, h_start, h_end)

Where Valid(d) is a boolean function returning TRUE if day d is not a weekend or holiday. The Overlap function calculates the milliseconds strictly within the working window:

Overlap = min(t_end, work_end) − max(t_start, work_start)

This ensures that work performed before 09:00 or after 17:00 is automatically discarded, while lunch breaks or partial days are accounted for if configured.

Reference Data

Time Unit / Cycle	Symbol	Category	Duration (Seconds)	Duration (Decimal Days)
Planck Time	t_P	Physics (Quantum)	5.39 × 10^-44	~0
Yoctosecond	ys	SI Prefix	1.0 × 10^-24	~0
Jiffy (Physics)	j	Physics	3.33564 × 10^-24	~0
Attosecond	as	SI Prefix	1.0 × 10^-18	~0
Femtosecond	fs	SI Prefix	1.0 × 10^-15	~0
Picosecond	ps	SI Prefix	1.0 × 10^-12	~0
Nanosecond	ns	SI Prefix	1.0 × 10^-9	~0
Microsecond	µs	SI Prefix	0.000001	~0
Shake	sh	Nuclear Physics	1.0 × 10^-8	~0
Millisecond	ms	SI Prefix	0.001	1.157 × 10^-8
Jiffy (Electronics)	j	Computing	0.0167 (60Hz)	1.9 × 10^-7
Second	s	Base SI	1	1.157 × 10^-5
Minute	min	Common	60	0.000694
Moment	mom	Medieval	90	0.00104
Ke (Quarter)	ke	Traditional Chinese	864	0.01
Kilosecond	ks	SI Prefix	1,000	0.01157
Hour	h	Common	3,600	0.04166
Watch	w	Nautical	14,400	0.1666
Day (Sidereal)	d_sid	Astronomy	86,164.09	0.99727
Day (Solar)	d	Common	86,400	1.0
Sol	sol	Martian Day	88,775.24	1.0275
Week	wk	Common	604,800	7.0
Megasecond	Ms	SI Prefix	1,000,000	11.57
Fortnight	fn	Common	1,209,600	14.0
Lunar Month	mo_syn	Astronomy	2,551,442.9	29.5306
Month (Gregorian)	mo	Average	2,629,746	30.4368
Quarantine	q	Historical	3,456,000	40.0
Semester	sem	Academic	~10,886,400	~126
Year (Lunar)	a_lun	Calendar	30,617,314	354.37
Year (Common)	yr	Calendar	31,536,000	365.0
Year (Tropical)	a_trop	Astronomy	31,556,925	365.242
Year (Julian)	a	Astronomy	31,557,600	365.25
Year (Sidereal)	a_sid	Astronomy	31,558,149.76	365.256
Year (Leap)	yr_leap	Calendar	31,622,400	366.0
Olympiad	ol	Historical	126,230,400	1,461
Lustrum	lust	Roman	157,788,000	1,826.25
Decade	dec	Common	315,576,000	3,652.5
Gigasecond	Gs	SI Prefix	1,000,000,000	11,574
Indiction	ind	Roman/Medieval	473,364,000	5,478.75
Jubilee	jub	Biblical	1,577,880,000	18,262.5
Century	c	Common	3,155,760,000	36,525
Millennium	kyr	Common	31,557,600,000	365,250
Megaannum	Ma	Geology	3.155 × 10¹³	3.65 × 10⁸
Cosmic Year	GY	Astronomy	7.1 × 10¹⁵	8.2 × 10¹⁰
Kalpa	kalpa	Hindu Cosmology	1.36 × 10¹⁷	1.57 × 10¹²

Frequently Asked Questions

Yes. The "Work Hours" mode is specifically designed for this. By setting your shift (e.g., 09:00 to 17:00) and enabling the filter, the calculator ignores nights, weekends, and early mornings. If a project starts Friday at 16:00 and ends Monday at 10:00, the tool correctly calculates 2 working hours (1 on Friday, 1 on Monday), whereas a standard calculator would show ~66 hours.

We use the browser's native JavaScript `Date` engine which utilizes the system's localized ICU (International Components for Unicode) data. This implies full support for Gregorian leap year rules (every 4 years, except 100, unless 400). Leap seconds are generally smoothed by the operating system (Unix time ignores them), so results are consistent with standard POSIX timekeeping.

Currently, the "Chain" mode supports adding/subtracting absolute time units (e.g., -3 weeks, +12 hours). Subtracting "working hours" specifically to find a start date is a reverse-business-logic feature that requires iterative solving. For now, use the "Chain" mode for calendar duration or the "Work Hours" mode to verify a specific span.

The Unix Epoch (Jan 1, 1970) provides a fixed reference point 0. By converting all dates to the number of milliseconds elapsed since this instant, we convert complex calendar math into simple integer arithmetic, eliminating off-by-one errors common in manual calculation.