# Get the total number of days in a year

Return 366 for Gregorian leap years and 365 otherwise.

Canonical: https://1loc.dev/date-time/get-the-total-number-of-days-in-a-year/
Version: 1.0.0
Runtime: JavaScript · Node.js 22 / modern browsers
Verification: Local fixtures; no external services
Updated: 2026-10-28

## Implementation

```javascript
function daysInYear(year) { return (year % 4 === 0 && year % 100 !== 0) || year % 400 === 0 ? 366 : 365; }
```

## Input

```json
2024
```

## Expected output

```json
366
```

## Edge case

Input:
```json
1900
```
Output:
```json
365
```

## Limits

- Proleptic Gregorian rules: 1900 is not a leap year, 2000 is.

The lab validates types and size before calling this function. Add equivalent validation at your own trust boundary.

## Source and license

Original: https://github.com/phuocng/1loc/blob/14b481cf60dff1620ab1bb99a43b1f68068cdd9b/contents/get-the-total-number-of-days-in-a-year.mdx
Author: Nguyen Huu Phuoc and original contributors
Contributors: See original repository history
Source commit: 14b481cf60dff1620ab1bb99a43b1f68068cdd9b
Copyright (c) 2020 phuoc-ng
License: MIT — https://1loc.dev/licenses/
Maintainer: Oveyon
Modifications: Keeps the arithmetic variant. Original MDX retained as inert source evidence.