Guides

How to Read and Use 24-Hour TimeStop mistaking 13:00 for 1:00 PM? Here is how to read, convert, and use 24-hour time, with a handy reference table. The most common mistake people mak How Calendars Shaped Modern ComputingHow the Gregorian calendar became the global computing standard, from the Julian reform to Unix time, ISO 8601, and CLDR localization. How Different Countries Write the DateEvery common written date puts day, month, and year in one of three orders. Borrowing a term from computing, these are described by their endianness What Is the Day of Year and How Is It Used?What day of the year is it right now? Ordinal date (day 1–366) vs. Julian Date explained. How day of year is used in manufacturing, logistics, How Daylight Saving Time Works Around the WorldA Berlin colleague emails at 9:00 AM her time. You are in New York. Is it 3:00 AM, 4:00 AM, or something else? The answer depends on the date, the hem Why Do Some Time Zones Have 30-Minute Offsets?Why do some countries have time zones offset by 30 or 45 minutes? India, Iran, Nepal, and others use non-standard offsets. Learn why. How Your Browser Knows What Time It IsOpen your browser. Look at the clock. That number didn't come from the internet. Your machine already knew it. How Your Browser Knows What Time It Is How the Network Time Protocol Keeps Your Clock in SyncYour system clock drifts the moment it leaves the factory. A cheap crystal oscillator loses a couple of seconds a day. A machine running 24/7 can be o What Is ISO 8601 and Why Does It Matter?ISO 8601 is published by the International Organization for Standardization, maintained by ISO TC 154. First released in 1988, it merged several earli How ISO Week Numbers WorkWhat is the current ISO week number and how is it calculated? The current ISO week number is determined by a single rule: Week 1 is the week containin Common JavaScript Date Pitfalls and How to Avoid ThemYour JavaScript dates are off by one hour because the Date object stores a single moment as UTC milliseconds, but every display method applies your sy What Are Leap Seconds and Why Do We Need Them?The second is defined by atomic physics. Since 1967, one second has been the duration of 9,192,631,770 periods of radiation from a caesium atom. Why Leap Years Exist and How They Affect TimekeepingWhy do we have leap years? The astronomical cause, the Gregorian rule, and what every programmer needs to know about February 29. RFC 2822 vs ISO 8601: Which Date Format Should You Use?Open a raw email and the Date: header reads Wed, 29 Jul 2026 03:14:07 +0000 . That shape is RFC 2822, frozen in place since 2001. How to Schedule Meetings Across Time ZonesLearn to schedule meetings across time zones using UTC, avoid DST traps, and communicate times clearly. Includes a quick reference checklist. What Happens When the Clocks Change for DST?What happens to the clock when DST starts and ends? The missing hour, the duplicate hour, and how computers handle the mess. Should You Always Store Dates in UTC?Past events are instants. Future events are local times. Store the fact you need, and let the zone rules do their work when the event happens. The Year 2038 Problem ExplainedA calendar entry for a routine Tuesday morning meeting. A database recording a payment. A factory controller logging a production milestone. How Different Databases Handle Time and Time ZonesHow MySQL, PostgreSQL, and SQLite handle timestamps and time zones. Compare TIMESTAMP vs DATETIME, WITH TIME ZONE vs WITHOUT, and SQLite's storage tri Timestamps vs Datetimes: Understanding the Key DifferenceA timestamp is an unambiguous instant; a datetime is a wall-clock value without a zone. Learn the difference, when to use each, and how databases trea What Is Unix Epoch Time?Open a browser console and type Date.now() . You get a thirteen-digit integer. That number is the current Unix epoch time in milliseconds: the count What Is a UTC Offset and How Do I Find Mine?Open a browser console. Type new Date().getTimezoneOffset() and press Enter. The number you see is minutes behind UTC. A negative result means you are What Is Coordinated Universal Time (UTC)?UTC is the world's time standard. Learn how it differs from GMT, how it's maintained by atomic clocks, and why it matters for computing and travel. Why Your Device's Clock Changes AutomaticlyYour computer clock changes automatically because of NTP time sync, DST rules, and time zone detection. Here is how they work and how to fix issues. Why You Shouldn't Trust Time Zone AbreviationsA 9 AM meeting written as "EST" lands 15 hours away from where you intended if the reader is in Sydney instead of New York. Why Your Timestamps Are Wrong and How to Fix ThemTimestamps off by one hour? Fix DST, database zone mismatch, and JavaScript parsing bugs. Step-by-step solutions for Node.js, Python, MySQL, and Postg