Picking the best RTC module for Arduino and ESP32 projects comes down to a question that’s easy to get wrong on a first build: how much accuracy does your project actually need, and does it even need a dedicated RTC chip at all. Plenty of tutorials reach for the classic DS1307 out of habit, when a DS3231 costs barely more and drifts dramatically less, and plenty of ESP32 projects buy an RTC module they didn’t need because a WiFi connection could have handled timekeeping for free.
This guide covers four RTC modules spanning the real differences that matter: chip accuracy, voltage compatibility, and build quality between a generic clone and a reference-quality breakout. If your project logs data, runs on a schedule, or needs to remember the time through a power loss, this is the component that makes that possible.
Wiring an RTC alongside other I2C sensors on the same bus? Our Best Logic Level Converter for Arduino and ESP32 guide covers what to do when a 5V Arduino needs to share that bus with 3.3V hardware, and Best Relay Module for Arduino and ESP32 covers a common project an accurate RTC pairs well with, like a scheduled irrigation or lighting controller.
Quick Comparison Table
| RTC Module | Chip | Accuracy | Voltage | Best For |
|---|---|---|---|---|
| HiLetgo DS3231 (AT24C32) | DS3231 | ±2ppm (~1 min/year) | 2.3V–5.5V | Best overall/accurate budget RTC |
| DS1307 Module | DS1307 | No temp compensation, several min/month drift | 5V only | Best classic/historically documented RTC |
| DONGKER PCF8523 Board | PCF8523 | ~2 sec/day (no temp compensation) | 3.3V–5V | Best low-power alternative chip family |
| Adafruit DS3231 Precision RTC | DS3231 | ±2ppm (~1 min/year) | 3.3V or 5V | Best premium/reference-quality RTC |
1. Best Overall/Accurate Budget RTC: HiLetgo DS3231 RTC Module
HiLetgo DS3231 RTC Module with AT24C32 EEPROM
Best for: Most Arduino and ESP32 projects that need real, dependable timekeeping without paying premium prices.
The DS3231 chip is the reason this module outperforms older RTC designs by a wide margin: it has a temperature-compensated crystal oscillator built directly into the chip package, which corrects for the timing drift that temperature changes cause in a standard external crystal. The result is accuracy rated at ±2ppm between 0°C and 40°C, which works out to roughly one minute of drift per year, a dramatic improvement over chips that lack that compensation.
This particular module bundles in an AT24C32 EEPROM chip alongside the RTC, giving you 32Kb of non-volatile storage on the same board for logging data alongside timestamps. It runs natively from 2.3V to 5.5V, so it works directly with a 3.3V ESP32 or a 5V Arduino without needing a level shifter, and the standard coin cell backup keeps it ticking through power loss.
Specifications:
- Chip: DS3231 with integrated TCXO (temperature-compensated crystal oscillator)
- Accuracy: ±2ppm from 0°C to 40°C, approximately ±1 minute per year
- Onboard EEPROM: AT24C32 (32Kb)
- Interface: I2C
- Voltage: 2.3V to 5.5V (works natively with 3.3V and 5V logic)
- Battery backup: CR2032 coin cell
Why it stands out:
- Genuinely accurate timekeeping thanks to the DS3231’s built-in temperature compensation
- Native 3.3V to 5.5V operation works with both Arduino and ESP32 without a level shifter
- Onboard EEPROM adds useful storage for data logging projects at no extra cost
- Two programmable alarms and a square-wave output for interrupt-driven timing
- Cheapest way to get DS3231-level accuracy in a breadboard-friendly module
Things to keep in mind:
- Generic clone manufacturing quality varies more than a branded breakout, check reviews for your specific batch
- CR2032 coin cell backup needs replacing every few years depending on usage
- EEPROM and RTC share the same I2C bus at different addresses, worth confirming no address conflicts with other I2C devices
👉 Buy HiLetgo DS3231 RTC Module on Amazon
Verdict: The right default RTC for nearly any Arduino or ESP32 project. Real DS3231 accuracy, native dual-voltage support, and bonus EEPROM storage at a low price.
2. Best Classic/Historically Documented RTC: DS1307 RTC Module
DS1307 RTC Module
Best for: Following an older tutorial that specifically calls for a DS1307, or projects where a few minutes of drift per month truly doesn’t matter.
The DS1307 is the RTC chip that shows up in the oldest and most numerous Arduino tutorials, largely because it was one of the first widely available, affordable real-time clocks for hobbyist use. It lacks the DS3231’s temperature-compensated oscillator entirely, relying on a standard external crystal, which means its timekeeping drifts noticeably more as ambient temperature changes throughout the day.
One detail that catches ESP32 users off guard: the DS1307 requires a 5V supply to operate correctly, unlike the DS3231, which runs natively on 3.3V. Powering it from an ESP32’s 3.3V rail directly is not a reliable substitute, and mixing 5V logic onto a 3.3V ESP32’s I2C bus without consideration is exactly the kind of problem a logic level converter exists to solve. For plain 5V Arduino projects, none of that matters, and the DS1307 remains a fine choice.
Specifications:
- Chip: DS1307, no temperature compensation
- Accuracy: drifts several minutes per month under varying temperature, more than the DS3231
- Interface: I2C
- Voltage: 5V required
- Onboard storage: 56 bytes of battery-backed general purpose RAM
- Battery backup: coin cell (varies by board)
Why it stands out:
- Massive legacy tutorial and library base going back to Arduino’s early days
- Cheap and widely available from nearly every electronics supplier
- 56 bytes of battery-backed RAM for small amounts of persistent data beyond just time
- Simple I2C wiring identical in pattern to the DS3231
- Fine accuracy for projects where minutes of drift per month don’t matter
Things to keep in mind:
- Requires a genuine 5V supply, doesn’t run natively on a 3.3V ESP32 like the DS3231 does
- No temperature compensation means noticeably more drift than the DS3231 in real-world conditions
- No onboard EEPROM the way the HiLetgo DS3231 module includes
👉 Buy DS1307 RTC Module on Amazon
Verdict: A fine choice for 5V Arduino projects that don’t need DS3231-level precision, but the DS3231 modules in this guide cost barely more for meaningfully better accuracy and 3.3V compatibility.
3. Best Low-Power Alternative Chip Family: DONGKER PCF8523 RTC Board
DONGKER PCF8523 RTC Board
Best for: Projects already built around the PCF8523 chip family, or anyone who wants a wide-voltage RTC with a pre-crimped connector instead of solder headers.
The PCF8523 is a completely different chip family from the DS3231 and DS1307, developed by NXP rather than Maxim/Analog Devices, and it’s the chip Adafruit reaches for in several of their own low-power kits. Like the DS1307, it lacks temperature compensation, so accuracy sits in a similar tier, typically able to gain or lose up to about 2 seconds a day rather than the DS3231’s roughly 1 minute per year.
This particular board runs on a flexible 3.3V to 5V supply, so it works natively with either an Arduino or an ESP32 without extra circuitry. Instead of the 0.1-inch header pins used by the other modules in this guide, it connects through an XH2.54-5P pre-crimped connector, the kind commonly used on sensor cables in this hobby, which is worth checking against your existing wiring before ordering if you’re used to breadboard-style headers.
Specifications:
- Chip: PCF8523, no temperature compensation
- Accuracy: approximately ±2 seconds per day
- Interface: I2C
- Voltage: 3.3V to 5V
- Connector: XH2.54-5P male pin (pre-crimped cable style, not standard 0.1-inch headers)
Why it stands out:
- Genuinely different chip family from DS3231/DS1307, useful if a project’s library or design already targets PCF8523
- Flexible 3.3V to 5V operation works with Arduino and ESP32 alike
- Low power draw makes it a reasonable fit for battery-powered projects
- XH2.54-5P connector suits builds already using pre-crimped cable harnesses
- Simple, inexpensive way to add battery-backed timekeeping to a project
Things to keep in mind:
- Accuracy sits closer to the DS1307’s tier than the DS3231’s, no temperature compensation onboard
- XH2.54-5P connector isn’t breadboard-friendly out of the box, plan for that if your build uses breadboards
- No onboard EEPROM or extra memory beyond basic timekeeping
👉 Buy DONGKER PCF8523 RTC Board on Amazon
Verdict: A reasonable pick specifically for projects already using PCF8523-based code or cabling, but the DS3231 modules above offer meaningfully better accuracy for a similar price if you’re starting from scratch.
4. Best Premium/Reference-Quality RTC: Adafruit DS3231 Precision RTC Breakout
Adafruit DS3231 Precision RTC Breakout
Best for: Builds where reliable battery backup and long-term dependability matter more than saving a few dollars on a generic clone.
This is the same DS3231 chip found in the HiLetgo module above, with the same ±2ppm accuracy and roughly one-minute-per-year drift. What differs is manufacturing quality and support: Adafruit’s breakout is built with support circuitry that properly handles both 3.3V and 5V logic levels, extensively documented with wiring guides and a mature Arduino library, and multiple real buyer reviews specifically note that cheaper clone boards sometimes fail to actually hold time on battery backup once main power is removed, while this one reliably does.
That reliability shows up in the small details clone boards sometimes get wrong: proper battery-backup circuit design so the RTC actually keeps ticking on the coin cell rather than silently resetting, consistent I2C timing, and a silkscreen that’s actually legible when you’re wiring it at a bench. For a clock, data logger, or any project where “did the time actually survive the power outage” matters, that reliability is worth the premium.
Specifications:
- Chip: DS3231 with integrated TCXO
- Accuracy: ±2ppm from 0°C to 40°C, approximately ±1 minute per year
- Interface: I2C
- Voltage: works with 3.3V (Feather/Raspberry Pi) or 5V (Arduino) logic levels
- Battery backup: CR1220 coin cell (not included)
Why it stands out:
- Same DS3231 accuracy as the generic clone modules, with meaningfully better build quality
- Verified reliable battery-backup circuit, a detail cheaper clones sometimes get wrong
- Extensive official documentation and a well-maintained Arduino/CircuitPython library
- Clean, legible silkscreen and consistent manufacturing from batch to batch
- Long track record as a reference design cited across the hobbyist community
Things to keep in mind:
- Costs more than the generic HiLetgo DS3231 module for the same core chip and accuracy
- CR1220 coin cell is smaller and less commonly on hand than the CR2032 used by many clones
- No onboard EEPROM, unlike the HiLetgo module that bundles one in
👉 Buy Adafruit DS3231 Precision RTC Breakout on Amazon
Verdict: The pick when you’ve been burned by a clone board losing time before, or when a project’s reliability matters enough to pay for known-good manufacturing.
Which RTC Module Should You Buy?
The right RTC module for Arduino or ESP32 comes down to two questions: how much timekeeping accuracy does the project actually need, and does your board even need a dedicated RTC chip in the first place.
For the vast majority of projects, the HiLetgo DS3231 module is the right starting point, genuine temperature-compensated accuracy, native dual-voltage support, and bonus EEPROM storage at a low price. If you’re specifically following an older tutorial built around the DS1307, or building a simple 5V-only Arduino project where drift truly doesn’t matter, the DS1307 module still does the job. The DONGKER PCF8523 board makes sense mainly if a project’s code or cabling already targets that specific chip family.
If reliability matters more than price, particularly for a clock or data logger where losing the time on a power outage would be a real problem, the Adafruit DS3231 Precision RTC Breakout is worth the premium over a generic clone. It’s the same core chip and accuracy as the HiLetgo module, built to a standard where the battery backup actually works the way it’s supposed to.
Why Accuracy Varies So Much Between RTC Chips
Every RTC chip in this guide keeps time using a 32.768kHz crystal oscillator, the same basic component found in a quartz wristwatch, but how each chip handles that crystal explains the accuracy differences between them.
A standard crystal oscillator, the kind used in the DS1307 and PCF8523, changes its oscillation frequency very slightly as temperature changes. That effect is small on its own, but it accumulates over time into real, noticeable drift, several minutes a month for the DS1307, or a couple of seconds a day for the PCF8523, depending on how much the ambient temperature actually swings around the device.
The DS3231 solves this by moving the crystal inside the chip package itself, alongside a built-in temperature sensor and compensation circuitry. As temperature shifts, the chip actively adjusts its internal timing to counteract the crystal’s natural drift, which is why it’s rated at ±2ppm across a 0°C to 40°C range instead of the much looser tolerances of an uncompensated design. That’s the entire reason a DS3231 module costs only slightly more than a DS1307 or PCF8523 board but delivers dramatically better real-world accuracy.
Do You Even Need a Dedicated RTC Module? NTP vs. Battery-Backed Timekeeping
Here’s a useful question worth asking before buying any RTC module: if your project is an ESP32 or ESP8266 with WiFi access, does it actually need one at all?
A WiFi-connected board can fetch the current time over the internet using NTP (Network Time Protocol), the same system computers and phones use to stay synchronized. Once connected, an ESP32 can pull accurate time directly from an NTP server with no additional hardware, no drift to worry about, and no coin cell battery to eventually replace. For projects that are always within WiFi range and only need the time while actively running, like a digital clock display, this eliminates the RTC module entirely.
Where a dedicated RTC module still earns its place is everywhere NTP falls short. A standalone Arduino Uno has no WiFi at all, so it has no path to network time whatsoever. A data logger deployed somewhere without reliable WiFi needs to keep accurate timestamps independent of any connection. And any project that needs to remember the correct time immediately after a power loss, before WiFi has even reconnected, needs a battery-backed RTC chip ticking in the background the whole time. The practical rule: if a project is WiFi-connected and only needs time while it’s actively running, NTP alone might save you a purchase. If it runs offline, logs data independently, or needs to survive a power cycle with the correct time intact, a hardware RTC module is still the right tool.
Final Recommendation
For most Arduino and ESP32 projects, the HiLetgo DS3231 module remains the best all-around choice for an RTC module for Arduino builds: genuine temperature-compensated accuracy, native 3.3V/5V support, and bundled EEPROM storage at a low price. Projects where reliability is worth paying for should step up to the Adafruit DS3231 Precision RTC Breakout instead, and WiFi-connected ESP32 projects should consider whether NTP alone might skip the need for an RTC module entirely.
ArduinoYard has two guides that pair directly with this topic: the DS3231 RTC Module with Arduino: A Complete Guide covers wiring, alarms, and sleep mode for the exact chip recommended above, and the ESP32 Digital Clock with OLED Display Using NTP walks through the WiFi-based alternative discussed in the section above, useful if you’re still deciding whether you need an RTC module at all.
Rounding out your Arduino and ESP32 parts bin? Check out our guides on the Best Logic Level Converter for Arduino and ESP32, Best Relay Module for Arduino and ESP32, and Best Arduino Sensor Kit.