Chalarangelo/30-seconds-of-code

---
title: Get the first or last date of a month using JavaScript
shortTitle: First or last date of a month
type: story
language: javascript
tags: [date]
cover: polar-bear
excerpt: Use the `Date` object and some clever tricks to get the first or last date of a month in JavaScript.
listed: true
dateModified: 2024-02-17
---

Getting the first date of a month is usually pretty simple. But how about getting the last date of a month? Here's how you can do both using JavaScript.

## Get the first date of a month

Given any `Date` object, you can use `Date.prototype.getFullYear()` and `Date.prototype.getMonth()` to get the **current year and month** from the given date. In order to get the first date of a month, you just need to create a new `Date` object, using these methods, and **set the day** to `1`.

```js
const firstDateOfMonth = (date = new Date()) =>
  new Date(date.getFullYear(), date.getMonth(), 1);

firstDateOfMonth(new Date('2015-08-11')); // '2015-08-01'
```

## Get the last date of a month

In order to get the last date of a month, we can use a clever trick on top of the previous snippet. Instead of setting the day to `1`, we can set it to `0`. This will give us the **last day of the previous month**. In order for this to work, we'll need to **advance the month** by `1` as well.

```js
const lastDateOfMonth = (date = new Date()) =>
  new Date(date.getFullYear(), date.getMonth() + 1, 0);

lastDateOfMonth(new Date('2015-08-11')); // '2015-08-31'
```