Source: https://mokxi.com/libraries/timelib Updated: 2026-11-02 Libraries / Data and time Arduino library · Data and time # TimeLib: a date and time kept by the Arduino itself The Time library, included as TimeLib.h, keeps the date and time in software. You set it once with setTime(), or give it a source with setSyncProvider() (a real-time clock, a GPS or an NTP request), and from then on it counts forward from millis(). hour(), minute(), second(), day(), month(), year() and weekday() read the current time; each also takes a time_t to read a stored one. Open the example in the editor See the calls Built in on Mokxi: #include and it builds, with nothing to install. Free, and no account needed. ## What Time does Time is held as a time_t, the number of seconds since January 1, 1970 (Unix time), which makes arithmetic easy: add 3600 for an hour, or subtract two times for the gap. makeTime() builds a time_t from a tmElements_t of fields, and breakTime() goes the other way. The helpers dayStr() and monthStr() turn numbers into names. Without a sync provider the clock is only as good as the board’s crystal or resonator, and it starts over at power-up. A sync provider is called at start and then every 300 seconds by default; setSyncInterval() changes that. Library Manager name | Time Author | Michael Margolis, Paul Stoffregen Include | #include Boards | every board Mokxi compiles for but ATtiny85 In the simulator | Simulated: it runs against the part the way it does on the bench. ## Install it It builds on every board Mokxi compiles for but ATtiny85. In Mokxi it is built in: #include and the sketch compiles, with no download, no zip and no Library Manager. On a real board, install "Time" by Michael Margolis, Paul Stoffregen from the Arduino IDE’s Library Manager (Sketch, Include Library, Manage Libraries), or add Time to lib_deps in PlatformIO. Mokxi follows the calls of release 1.6.1, so a sketch written here builds there too. ESP32-C3 · Arduino Uno · Arduino Nano · Arduino Mega 2560 · Arduino Leonardo · SparkFun Pro Micro · Arduino Micro · ESP32-C6 · Raspberry Pi Pico · Raspberry Pi Pico W · Seeed XIAO SAMD21 · STM32 · STM32 Nucleo-F411RE · STM32 Blue Pill · micro:bit V2 · Arduino Uno R4 · ESP32 DevKit · ESP32-S3-DevKitC-1 · ESP8266 NodeMCU · Arduino Pro Mini 3.3 V · Seeed XIAO ESP32-C3 · ESP32-C3 SuperMini · Seeed XIAO ESP32-C6 · ESP32-DevKitC V4 · LOLIN32 Lite · Wemos D1 R32 · Cheap Yellow Display · TTGO T-Display · Seeed XIAO ESP32-S3 · Arduino Nano ESP32 · Arduino Nano RP2040 Connect · Seeed XIAO RP2040 · Waveshare RP2040-Zero · Arduino Uno R4 WiFi ## The calls you will use In the order a sketch meets them. ### setTime(12, 30, 0, 1, 10, 2026) Sets the clock: hour, minute, second, day, month, year. setTime(t) takes a time_t instead. ### hour() The current hour, 0 to 23. minute(), second(), day(), month(), year() and weekday() (1 is Sunday) work the same way. ### time_t t = now(); The current time as seconds since 1970. Read it once and pass it to hour(t), minute(t) and friends so every field comes from the same second. ### tmElements_t tm; A time split into Second, Minute, Hour, Wday, Day, Month and Year (counted from 1970). ### time_t t = makeTime(tm); Builds a time_t from the fields in tm. ### breakTime(t, tm) Splits a time_t back into the fields of tm. ### setSyncProvider(getRtcTime) Gives the library a function that returns the true time as a time_t, called at start and every sync interval. ### setSyncInterval(60) How many seconds between calls to the sync provider. ### timeStatus() timeNotSet, timeNeedsSync or timeSet, so the sketch can tell a real time from one that was never set. ### adjustTime(3600) Shifts the clock by that many seconds, for example to apply a time zone by hand. ## Example: A clock that keeps time on millis() On the Arduino Uno R3. It runs in the browser exactly as printed. sketch.ino · Arduino Uno R3 Open it in the editor, wired and ready to run ## Common errors and how to fix them ### fatal error: Time.h: No such file or directory, or the wrong Time.h is used The library’s header is TimeLib.h. Older tutorials include Time.h, which clashes with the C library’s time.h on systems that ignore case. Change the line to #include . ### The clock starts at 00:00:00 January 1, 1970 on every reset Nothing set the time after power-up. Call setTime() in setup(), or attach a real-time clock with setSyncProvider() so the time comes back after a reset. ### The clock gains or loses minutes over a day Without a sync provider the time is only as good as the board’s oscillator, and a ceramic resonator can drift a lot. Sync from an RTC module or NTP every few minutes. ## Keep going ### Learn - Arduino millis(): Timers and Multiple Tasks - Arduino millis() Overflow: Why Subtraction Works ### More data and time libraries - QRCode - Madgwick - PID - TimerOne - MsTimer2 - Low-Power - RTClib - DS1307RTC Every built-in library · Open the editor ## Try Time without installing anything Open the example, change the sketch, and keep your version in a free account. Start building free Open the editor