Unix Timestamp Converter
Convert units with the Unix Timestamp Converter — enter a value and get accurate converted results instantly using verified formulas.
Calculator
Adjust values & calculateSeconds or milliseconds since Jan 1, 1970 UTC
Timezones
Formula
A Unix timestamp is the total number of seconds elapsed since the Unix epoch (January 1, 1970 00:00:00 UTC). To convert a timestamp to a date, add that many seconds to the epoch. To convert a date to a timestamp, calculate the difference in seconds between the date and the epoch. Millisecond timestamps multiply the seconds value by 1000 for sub-second precision.
Last reviewed: December 2025
Worked Examples
Example 1: Convert Timestamp to Date
Example 2: Convert Date to Timestamp
Background & Theory
The Unix Timestamp Converter applies the following established principles and formulas. Date and time calculations underpin a vast range of applications from financial settlement to scheduling and age verification. The complexity arises because civil timekeeping uses irregular units: months have 28, 29, 30, or 31 days; years have 365 or 366 days; hours, minutes, and seconds use base-60 arithmetic; and time zones introduce offsets ranging from -12:00 to +14:00 relative to UTC. The Gregorian calendar's leap year rule is a compound condition: a year is a leap year if it is divisible by 4, except for century years, which must be divisible by 400. Thus 1900 was not a leap year but 2000 was. This rule keeps the calendar synchronized with the solar year to within about 26 seconds per year. For algorithmic date calculations, the Julian Day Number provides a continuous integer count of days since January 1, 4713 BCE, eliminating the irregularity of calendar months and making interval arithmetic straightforward. The Unix epoch, by contrast, counts seconds since 00:00:00 UTC on January 1, 1970, and is the basis of POSIX time used in most computing systems. ISO 8601 standardizes date and time representation as YYYY-MM-DD and combined datetime as YYYY-MM-DDTHH:MM:SS±HH:MM, ensuring unambiguous machine-readable interchange across locales that would otherwise differ in day/month/year ordering. Business day calculation requires excluding weekends and, optionally, a jurisdiction-specific list of public holidays. Duration calculations expressed in years, months, and days must account for the variable length of months, making them non-commutative: the interval from January 31 to February 28 is different from the interval from February 28 to March 31. Age calculation algorithms must handle the edge case of birthdays on February 29 and ensure that a person born on December 31 is not counted as one year older on January 1 of the following year until the clock passes midnight. Zeller's Congruence provides a closed-form formula to determine the day of the week for any Gregorian or Julian calendar date using only integer arithmetic.
History
The history behind the Unix Timestamp Converter traces back through the following developments. The need to track time and predict astronomical events gave rise to calendrical systems independently across many civilizations. The Babylonians, around 2000 BCE, developed a lunisolar calendar with 12 months of alternating 29 and 30 days, inserting an intercalary month periodically to keep pace with the solar year. They also divided the day into 24 hours and the hour into 60 minutes, a sexagesimal convention that persists in every modern clock. The Egyptian civil calendar used 12 months of exactly 30 days plus five epagomenal days, totaling 365 days. Though simple for administrative purposes, it drifted against the solar year by one day every four years. Julius Caesar, advised by the Egyptian astronomer Sosigenes, reformed the Roman calendar in 45 BCE. The Julian calendar introduced a 365-day year with a leap day every four years, a system that served Europe for over sixteen centuries. By the 16th century, the accumulated error of the Julian calendar had shifted the spring equinox ten days from its ecclesiastically mandated date, disrupting the calculation of Easter. Pope Gregory XIII commissioned the calendar reform that bears his name, and the Gregorian calendar was introduced in Catholic countries in October 1582. The transition required skipping ten days: October 4 was followed by October 15. Protestant and Orthodox countries adopted the reform slowly; Britain and its colonies switched in 1752, Russia not until 1918, and Greece in 1923. The expansion of railways in the 1840s created an urgent practical problem: each city operated on its own local solar time, making train timetables impossible to coordinate. British railways adopted Greenwich Mean Time as a standard in 1847. The International Meridian Conference of 1884 in Washington formalized the prime meridian at Greenwich and established the global framework of 24 time zones. Daylight saving time was first adopted nationally during World War I to reduce coal consumption. The development of atomic clocks after World War II led to the definition of Coordinated Universal Time (UTC) in 1960, accurate to nanoseconds. The Y2K problem of 1999-2000 demonstrated that two-digit year storage in legacy systems could cause widespread failures, prompting a global remediation effort costing an estimated 300 to 600 billion dollars.
Frequently Asked Questions
Sources & References
Reviewed by Daniel Agrici, Founder & Lead Developer · Editorial policy
Unix Timestamp Converter Formula
Unix Timestamp = (Date - January 1, 1970 00:00:00 UTC) in seconds
A Unix timestamp is the total number of seconds elapsed since the Unix epoch (January 1, 1970 00:00:00 UTC). To convert a timestamp to a date, add that many seconds to the epoch. To convert a date to a timestamp, calculate the difference in seconds between the date and the epoch. Millisecond timestamps multiply the seconds value by 1000 for sub-second precision.
Unix Timestamp Converter — Worked Examples
Example 1: Convert Timestamp to Date
Problem: Convert Unix timestamp 1735689600 to a human-readable date.
Solution: 1735689600 seconds since Jan 1, 1970 UTC\n= 1,735,689,600 ÷ 86,400 = 20,088.5 days\n= 55 years + days\nResult: January 1, 2025 00:00:00 UTC
Result: January 1, 2025 00:00:00 UTC (Wednesday)
Example 2: Convert Date to Timestamp
Problem: What is the Unix timestamp for July 4, 2026 at 12:00 PM UTC?
Solution: From Jan 1, 1970 to July 4, 2026 = 20,638 days\n20,638 × 86,400 = 1,783,123,200 seconds\nPlus 12 hours = 43,200 seconds\nTotal: 1,783,166,400
Result: 1783166400 (seconds) | 1783166400000 (milliseconds)
Unix Timestamp Converter — Frequently Asked Questions
What is a Unix timestamp?
A Unix timestamp (also called Unix epoch time or POSIX time) is the number of seconds that have elapsed since January 1, 1970 at 00:00:00 UTC — known as the Unix epoch. It's a simple way to represent a point in time as a single number, making it easy to store, compare, and calculate time differences. For example, timestamp 1000000000 represents September 9, 2001 at 01:46:40 UTC. Unix timestamps are widely used in programming, databases, APIs, log files, and web development.
How do timezones affect Unix timestamps?
Unix timestamps are timezone-independent — they always represent a specific moment in UTC. The same timestamp displays as different local times depending on the timezone. For example, timestamp 1711036800 is March 22, 2024 00:00:00 UTC, but March 21, 2024 20:00:00 in New York (EDT, UTC-4). When converting a local date/time to a timestamp, the timezone must be considered. This converter shows the same timestamp in multiple timezones for easy comparison.
Can Unix timestamps represent dates before 1970?
Yes, dates before January 1, 1970 are represented by negative Unix timestamps. For example, December 31, 1969 23:59:59 UTC is timestamp -1, and January 1, 1900 00:00:00 UTC is approximately -2,208,988,800. JavaScript's Date object supports dates from April 20, 271821 BC to September 13, 275760 AD, well beyond what 32-bit systems allow. Negative timestamps are commonly used to represent historical dates in databases and scientific applications.
Why might my result differ from another tool or reference?
Differences typically arise from rounding conventions, the specific version of a formula (for example, simple vs compound interest), or unit inconsistencies between inputs. Check that both tools are using the same formula variant and the same units. The References section links to the authoritative source behind the formula used here.
Can I use the results for professional or academic purposes?
You may use the results for reference and educational purposes. For professional reports, academic papers, or critical decisions, we recommend verifying outputs against peer-reviewed sources or consulting a qualified expert in the relevant field.
Is my data stored or sent to a server?
No. All calculations run entirely in your browser using JavaScript. No data you enter is ever transmitted to any server or stored anywhere. Your inputs remain completely private.