Day.js vs Moment.js
Which should you use? A side-by-side look at what each one does, who it suits, what it costs, how hard it is to set up, and where each falls short.
Open source · MIT
A small JavaScript library for working with dates and times, with an API similar to Moment.js.
Open source · MIT
A JavaScript library for parsing, validating, manipulating and formatting dates; now in maintenance mode.
The short answer
Choose Day.js if you need…
- JavaScript developers who used Moment.js and want a smaller library
- Front-end projects where bundle size matters
- Apps that need date formatting and simple date arithmetic
- Projects that need localized date output via locale files
Choose Moment.js if you need…
- Maintaining existing JavaScript projects that already depend on Moment.js
- Developers who need a familiar date API and are not starting a new project
- Teams whose code already uses Moment and need bug-level upkeep
Side-by-side
| Day.js | Moment.js | |
|---|---|---|
| Type | Library | Library |
| Price | Free and open source | Free and open source |
| Licence | MIT | MIT |
| GitHub stars | 48.7k | 47.9k |
| Setup difficulty | Beginner | Beginner |
| How you get it | Install with a package manager | Install with a package manager |
| Main language | JavaScript | JavaScript |
| Last code update | 52 days ago | 29 days ago |
What each one is
Day.js
Day.js is a small JavaScript library (about 2kB, per the README) that parses, checks, changes, and formats dates and times. Its API is largely compatible with Moment.js, so people familiar with Moment.js can use it with little relearning. Its objects are immutable, so operations return new values instead of changing the original.
Moment.js
Moment.js is a JavaScript library that helps programs work with dates and times: reading date strings, checking whether they are valid, changing them (adding days, shifting time zones, and so on), and displaying them in readable formats. It is installed into a JavaScript project with npm, yarn, or bun. The README now marks it as a legacy project in maintenance mode, so it is not accepting new features.
Best for
Day.js
- JavaScript developers who used Moment.js and want a smaller library
- Front-end projects where bundle size matters
- Apps that need date formatting and simple date arithmetic
- Projects that need localized date output via locale files
Moment.js
- Maintaining existing JavaScript projects that already depend on Moment.js
- Developers who need a familiar date API and are not starting a new project
- Teams whose code already uses Moment and need bug-level upkeep
Strengths
Day.js
- Small footprint (about 2kB according to the README)
- Familiar API for anyone who has used Moment.js
- Immutable and chainable, which makes code easier to reason about
Moment.js
- Widely used, with a large community and many years of existing code and examples
- MIT licensed and distributed through npm
- Maintained under the OpenJS Foundation, which provides governance and a security policy
Not ideal for
Day.js
- Projects that need full timezone handling beyond what the README describes; the README does not detail timezone support, so check the docs first
- Non-JavaScript environments, since the library is written for JavaScript
- Users who need a graphical or no-code tool
Moment.js
- New projects: the README says new features are not being accepted, so newer date libraries may be a better long-term choice
- Users who need a tool with no programming involved, since this is a code library
Trade-offs
Day.js
- Some functionality is in optional plugins, which must be loaded separately
- Compatibility with Moment.js is described as largely, not complete, so some code may need changes
- Documentation and details live on the external site day.js.org rather than the README
Moment.js
- Maintenance mode: no new features are being accepted, so the library will not gain modern capabilities
- The README does not detail its size or performance trade-offs, so check those for your use case
Getting started
Frequently asked questions
What is the difference between Day.js and Moment.js?
Day.js: A small JavaScript library for working with dates and times, with an API similar to Moment.js. Moment.js: A JavaScript library for parsing, validating, manipulating and formatting dates; now in maintenance mode. Day.js suits javascript developers who used moment.js and want a smaller library, while Moment.js suits maintaining existing javascript projects that already depend on moment.js.
Are Day.js and Moment.js free?
Day.js: Free and open source. Moment.js: Free and open source.
Is Day.js or Moment.js more popular?
Day.js has more GitHub stars (48.7k) than Moment.js (47.9k). Popularity isn't the same as fit — check which one matches your use case above.
What are other alternatives to Day.js and Moment.js?
Other options people compare them with include Luxon, flatpickr.
Keep comparing
Built from our catalogue entries for both products: open-source details come from each project's README (AI-assisted, refreshed weekly) and GitHub data; AI-tool details are editorial. Spotted something wrong? Let us know from either product's page.