What is the difference between seconds, milliseconds, and microseconds in timestamps?

Seconds-precision timestamps (10 digits as of 2026) are the original Unix time standard used by POSIX systems, Linux file metadata, and many databases. Milliseconds-precision timestamps (13 digits) are used by JavaScript's Date.now(), Java's System.currentTimeMillis(), and many web APIs that need finer granularity for request timing, performance measurement, or event ordering. Microseconds-precision timestamps (16 digits) appear in high-frequency trading systems, scientific data collection, and Python's datetime objects (which have microsecond resolution). The key practical distinction: if you see a timestamp around 1,750,000,000, it is seconds. If you see a timestamp around 1,750,000,000,000, it is milliseconds. A factor-of-1000 error in identification produces dates that are 56 years off in either direction—159,362,180,000,000 is not the year 5044, it is just 159,362,180,000 milliseconds, which is approximately the year 1975. Our tool detects the magnitude and applies the correct divisor automatically, so you never need to guess.

Why does the converted date look one hour off from what I expected?

This is almost always a daylight saving time (DST) issue, not a bug in the converter. UTC is a continuous, uniform timescale that does not observe DST. Your local time, however, shifts forward by one hour in spring and back by one hour in autumn. For example, if it is July in New York (EDT = UTC-4), a timestamp representing 3:00 PM UTC displays as 11:00 AM local. If you expected noon, you might be mentally applying the winter offset (EST = UTC-5) instead of the summer offset. The converter shows both UTC and local time side by side with the exact UTC offset labelled (e.g., UTC-4 or UTC-5), so you can instantly verify which offset is being applied. If the offset is wrong for your location, check your computer's system timezone settings—browser-based tools derive the local timezone from your operating system, and an incorrectly configured system clock or timezone will produce unexpected local time displays.

Can I convert dates before 1970 using a Unix timestamp converter?

Yes. The Unix timestamp system supports negative numbers for dates before the epoch. January 1, 1970 at 00:00:00 UTC is timestamp 0. One second earlier—December 31, 1969 at 23:59:59 UTC—is timestamp -1. One day earlier (December 31, 1969 at 00:00:00 UTC) is timestamp -86400. Our converter handles negative timestamps correctly back to January 1, 1000 CE (timestamp -30610224000), which covers nearly all historical computing data. For dates earlier than 1000 CE, the proleptic Gregorian calendar (which extends the Gregorian calendar backward before its 1582 adoption) introduces increasing inaccuracy, and specialized historical date libraries should be used instead. Pre-1970 timestamps most commonly appear in genealogy databases, historical archives, legacy banking systems, and data imported from systems that were operational before the Unix epoch was standardized.

What is the Year 2038 problem and should I be worried about it?

The Year 2038 Problem (Y2038 or Y2K38) affects systems that store Unix timestamps as a signed 32-bit integer. In this representation, the maximum value is 2,147,483,647, which corresponds to January 19, 2038 at 03:14:07 UTC. One second later, the value overflows to -2,147,483,648, which represents December 13, 1901—a 136-year jump backward that will cause date calculations, comparisons, and displays to fail catastrophically. This is the same class of problem as the Y2K bug but with a different root cause. Systems at risk include: 32-bit embedded devices (routers, industrial controllers, older IoT hardware), legacy C/C++ programs compiled for 32-bit platforms that use the time_t type, older versions of PHP (before 5.6 on 32-bit), and 32-bit MySQL/MariaDB instances. Most modern systems—64-bit Linux, macOS, Windows, all major cloud platforms, current programming language runtimes, and recent database versions—use 64-bit timestamps and are immune (64-bit signed timestamps overflow in the year 292,277,026,596). If you maintain infrastructure, audit any 32-bit systems that handle dates and plan migration to 64-bit before 2038.

What is ISO 8601 format and why should I use it for dates in my API?

ISO 8601 is the international standard for representing dates and times, published by the International Organization for Standardization. The format looks like this: 2026-05-10T15:30:00Z (UTC) or 2026-05-10T15:30:00-04:00 (with timezone offset). It has several advantages that make it the best choice for API responses and data interchange. It is unambiguous: unlike regional formats (05/10/2026 could be May 10 or October 5 depending on locale), ISO 8601 always follows YYYY-MM-DD order, which no culture reverses. It is sortable as plain text: alphabetical sorting of ISO 8601 strings produces chronological order, making it ideal for log files and database indexes. It is timezone-explicit: the Z suffix means UTC, and numeric offsets like -04:00 clearly indicate the local time relationship. It is widely supported: JSON Schema, OpenAPI, JavaScript's Date.parse(), Python's datetime.fromisoformat(), and every major database can parse ISO 8601 natively. It separates date and time with T, avoiding the ambiguity of spaces in URLs and query strings. For these reasons, virtually every modern API style guide (Google, Microsoft, Stripe, GitHub) recommends ISO 8601 for date-time representations.

How do different programming languages handle Unix timestamps, and what should I watch out for?

Different languages return timestamps in different units and types, and mixing them up is a common source of bugs. JavaScript's Date.now() returns milliseconds as a number—if you pass it to a system expecting seconds, your dates will be 1,000 times too large (the year 50668 instead of 2026). Python's time.time() returns seconds as a float, with the integer part being seconds and the fractional part being sub-second precision—when you need milliseconds, multiply by 1,000 and round. Java's System.currentTimeMillis() returns milliseconds as a long. PHP's time() returns seconds as an integer; microtime() returns seconds as a float. Go's time.Now().Unix() returns seconds; time.Now().UnixMilli() returns milliseconds. Rust's SystemTime uses Duration since the epoch with nanosecond precision. The safest practice: when sending timestamps between systems, explicitly document the unit (seconds, milliseconds, or microseconds) in your API specification, and validate incoming timestamps by checking their magnitude—if a supposedly "seconds" timestamp is 13 digits, reject or convert it rather than silently computing a date in the year 50668.

Developer ToolsFeatured2026-05-10

How to Use a Unix Timestamp Converter – Epoch to Date Online

Computers do not understand "May 10, 2026 at 3:30 PM." They understand numbers—specifically, a single integer counting the seconds (or milliseconds) since a fixed reference point. That reference point is the Unix epoch: 00:00:00 UTC on January 1, 1970. The number 1751500800 does not look like anything to a human, but to a computer it unambiguously represents one exact moment in time, independent of timezone, daylight saving shifts, or calendar quirks. This elegant simplicity is why Unix timestamps are the dominant time representation in software: they appear in API responses (created_at: 1751500800), database timestamp columns, log files (every line prefixed with an epoch value), authentication tokens (iat and exp claims in JWTs), and virtually every system that needs to record when something happened. But the moment you need to debug a production incident, read an audit log, or verify that an API response contains the right date, those integer timestamps become a wall of meaningless digits. Our free timestamp converter eliminates that friction instantly. Paste any Unix timestamp—whether in seconds (10 digits), milliseconds (13 digits), or even microseconds (16 digits)—and the tool displays the equivalent human-readable date and time in both UTC and your local timezone. The ISO 8601 formatted output (e.g., 2026-05-10T15:30:00Z) is ready to drop into any API documentation, test fixture, or database query. Reverse conversion is equally simple: pick a date and time from the calendar picker and get the corresponding Unix timestamp immediately. Every computation happens in your browser with zero server communication, and the tool handles edge cases that many converters miss: negative timestamps for pre-1970 dates, the Year 2038 problem for 32-bit systems, and automatic detection of second vs. millisecond vs. microsecond precision.

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Timestamp Converter

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Step-by-Step Guide

Paste Your Unix Timestamp or Pick a Date from the Calendar

To convert a timestamp to a human-readable date, paste the integer into the input field. The tool automatically detects the precision based on the number's magnitude: a 10-digit number (roughly 1,000,000,000 to 2,000,000,000 as of 2026) is treated as seconds; a 13-digit number (roughly 1,700,000,000,000 to 1,800,000,000,000) is treated as milliseconds; a 16-digit number is treated as microseconds. This auto-detection eliminates the guesswork of "is this timestamp in seconds or milliseconds?"—a question that has caused countless off-by-factor-of-1000 bugs in production systems. If you have a timestamp in an unusual format (e.g., seconds as a decimal with fractional milliseconds), the tool parses it correctly and displays the precise time including fractional seconds. To convert a date to a timestamp, use the date and time picker to select any date from January 1, 1000 CE through December 31, 9999 CE. The equivalent Unix timestamp appears instantly as you adjust the date or time. You can also click "Use current time" to populate the picker with the present moment, useful for generating timestamps for API test requests or checking how long ago a particular log entry was created.

Read the Converted Date in Multiple Formats Simultaneously

The tool displays the converted result in three complementary formats so you pick exactly what you need. First, the human-readable date and time appears in your local timezone—for example, "Sunday, May 10, 2026 at 3:30:00 PM EDT"—with the UTC offset clearly labelled so there is no ambiguity about which timezone is being shown. Second, the UTC equivalent is displayed alongside it, because UTC is the universal reference that eliminates timezone confusion entirely. The side-by-side display lets you instantly verify whether a timestamp aligns with expectations: if an API says a user was created at 1751500800 and your local display shows 3:30 PM but UTC shows 7:30 PM, you know the timestamp is correct and the difference is just your timezone offset. Third, the ISO 8601 formatted string appears (e.g., 2026-05-10T15:30:00-04:00 or 2026-05-10T19:30:00Z for UTC), ready for immediate use in APIs, database queries, or documentation. ISO 8601 is the international standard for date-time representation and is the safest format for data interchange because it is unambiguous, sortable as plain text, and includes timezone information. A relative time description—"3 hours ago," "in 2 days," or "last Tuesday"—gives you immediate human context without mental math.

Copy the Output in Your Preferred Format or Use It in Your Code

Each output format has its own dedicated copy button—click the button next to the Unix timestamp (10-digit seconds), the millisecond timestamp (13-digit), the ISO 8601 string, or the human-readable date to copy that specific format to your clipboard. This lets you grab exactly what your code, database, or documentation needs without manually reformatting anything. For developers integrating timestamp conversion into their workflow, the tool serves as a quick reference for generating test data: want to test how your app handles an event 30 days in the future? Pick the date, copy the corresponding timestamp, and insert it into your test database. Need to verify that a JWT token's exp claim (expiration time) has not passed? Paste the exp timestamp and check the relative time display—if it says "in 5 minutes," the token is still valid. For log analysis, paste a series of timestamps from your log file to reconstruct the timeline of events in local time, making it far easier to correlate incidents with specific user actions. The tool also helps when writing date-related code: it validates that your timestamp-to-date conversions are correct by letting you manually verify the output against a known reference.

Tips & Best Practices

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A Unix timestamp in seconds is 10 digits from September 2001 through approximately November 2286 (covering a span of 285 years). Millisecond timestamps are 13 digits during the same period and will remain so until 2286. If your timestamp has 10 digits, it is almost certainly seconds; 13 digits means milliseconds; 16 digits means microseconds. The tool auto-detects this for you.

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JavaScript's Date.now() returns a millisecond-precision timestamp (13 digits). Python's time.time() returns a float with second precision and fractional microseconds (e.g., 1751500800.123456). Know what your language returns to avoid factor-of-1000 errors when integrating with other systems.

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Always store timestamps in UTC in your database. Convert to local time only at the presentation layer when displaying to users. This single practice prevents the majority of timezone-related production bugs—daylight saving time transitions, users moving across timezones, and servers in different geographic regions all become non-issues when your canonical data is UTC.

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ISO 8601 format (2026-05-10T15:30:00Z) is the safest choice for API responses and data interchange. It is human-readable, machine-parseable, timezone-explicit (Z = UTC, or an offset like -04:00), and sorts correctly as a plain string. JSON Schema and OpenAPI both recommend ISO 8601 for date-time fields.

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The Year 2038 Problem affects 32-bit signed integer timestamps: on January 19, 2038 at 03:14:07 UTC, the value reaches 2,147,483,647 (the maximum 32-bit signed integer) and overflows to a negative number, causing dates to jump back to December 1901. Modern 64-bit systems are immune (they can represent dates 292 billion years into the future), but embedded systems, legacy databases, and older IoT devices may still use 32-bit time_t. If you maintain C/C++ code that uses time_t on 32-bit platforms, plan to migrate to 64-bit before 2038.

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Negative timestamps represent dates before the Unix epoch (January 1, 1970). For example, timestamp -1 corresponds to December 31, 1969 at 23:59:59 UTC. The converter handles negative timestamps correctly back to January 1, 1000 CE, which is useful for historians, archivists, and anyone working with legacy data that predates the Unix era.

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When comparing timestamps from different systems, always check the unit. One system might log in seconds while another logs in milliseconds. A timestamp of 1751500800 (seconds) is May 10, 2026, but 1751500800 interpreted as milliseconds is only January 20, 1970—a difference of 56 years. If converted dates are wildly wrong, divide or multiply by 1000 as a first debugging step.

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For timezone conversions: UTC does not observe daylight saving time. If your local time display looks one hour off from your expectation, you are almost certainly seeing a DST effect. The tool shows both UTC and local time side by side so you can identify DST-related discrepancies instantly. Eastern Time, for example, is UTC-5 during standard time (EST, November-March) but UTC-4 during daylight time (EDT, March-November).

Frequently Asked Questions

A Unix timestamp (also called Unix time, epoch time, or POSIX time) is the number of seconds that have elapsed since 00:00:00 Coordinated Universal Time (UTC) on January 1, 1970—the Unix epoch. It does not count leap seconds; each day is treated as exactly 86,400 seconds. Unix timestamps are the dominant way computers store and exchange time because they have several powerful properties: they are a single integer requiring just 4 or 8 bytes of storage (much smaller than a date string like "2026-05-10T15:30:00+00:00"), they are timezone-agnostic (a timestamp represents the same instant everywhere in the world), they are trivially comparable (earlier times have smaller numbers, so sorting and range queries are simple comparisons), and arithmetic is straightforward (add 86,400 to advance one day; subtract two timestamps to measure elapsed seconds). These properties make Unix timestamps ideal for databases, API responses, log files, authentication tokens, file systems, and any system where dates must be stored, compared, or transmitted efficiently.

Unix timestamps are the backbone of time representation in software, but they are impenetrable without a reliable converter. Our free tool translates between timestamps and human-readable dates instantly, handles seconds/milliseconds/microseconds automatically, and displays results in both UTC and your local timezone. It works offline, keeps your data private, and requires no account. Bookmark it for your next log analysis, API debugging session, or database query. Try it now: paste any Unix timestamp and see the exact date and time.

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