Date.prototype.setDate() changes the day of the month of a Date according to local time. It mutates the object in place and returns the new epoch milliseconds.
date.setDate(dayOfMonth)
dayOfMonth = 1 … 31 for a normal day
dayOfMonth = 0 → last day of previous month
dayOfMonth = 32+ → overflows into next month
→ mutates date
→ returns new epoch ms (or NaN if invalid)Call date.setDate. Start with this line.
date.setDate(dateValue)| Call | What it does |
|---|---|
date.setDate(dateValue) | Primary signature. |
date.setDate(...) | Call with the arguments your case needs. |
Built into JavaScript. Call setDate(...) on a Date instance — no import required.
date.setDate(dateValue)| Parameter | Description |
|---|---|
| dateValue | Required. Day of month (integer; out-of-range OK) |
| Return Value | Description |
|---|---|
| * | New epoch ms (same as getTime()) |
Change the local day, then read it back with getDate().
const event = new Date("August 19, 1975 23:15:30");
event.setDate(24);
console.log(event.getDate()); // 24setDate(24) stores day 24.getDate() returns 24.event object is updated in place.Values past the month length roll forward automatically.
const event = new Date("August 19, 1975 23:15:30");
event.setDate(32); // August has 31 days
console.log(event.getDate()); // 1
console.log(event.getMonth()); // 8 (September; months are 0-indexed)32 is past August’s 31 days.getDate() is 1.getMonth() is 8 (September).getDate() + nThe usual pattern for “one week later” without a manual calendar table.
const d = new Date(2026, 0, 10); // Jan 10, 2026
d.setDate(d.getDate() + 7);
console.log(d.getDate()); // 17
console.log(d.getMonth()); // 0 (still January)getDate() is 10.10 + 7 → pass 17 to setDate.0.Date.prototype.setDate() is part of the language from early ECMAScript and is Baseline Widely available (MDN).
Supported in every modern browser and Node.js. No polyfill needed for ordinary web apps.
Bottom line: Safe everywhere. Focus on overflow rules and local vs UTC choice rather than feature detection.
Learn how to set the full year on a Date in local time.
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