How to add days, months or hours to a date

Short answer

setDate() with the current day plus N moves the date forward and rolls over to the next month itself:

const date = new Date(2025, 0, 29);
date.setDate(date.getDate() + 5);
 
console.log(date.toDateString());

Output:

Mon Feb 03 2025

Without changing the original

The setters change the date object itself. Make a copy first:

const addDays = (date, days) => {
  const result = new Date(date);
  result.setDate(result.getDate() + days);
  return result;
};
 
const today = new Date(2025, 5, 10);
const nextWeek = addDays(today, 7);
 
console.log(today.getDate(), nextWeek.getDate());

Output:

10 17

Months and years

setMonth() and setFullYear() work the same way:

const date = new Date(2025, 10, 15);
date.setMonth(date.getMonth() + 3);
 
console.log(date.toDateString());

Output:

Sun Feb 15 2026

Hours and minutes

For hours and minutes, use setHours() and setMinutes():

const date = new Date(2025, 0, 1, 22, 30);
date.setHours(date.getHours() + 3);
 
console.log(date.toDateString(), date.getHours() + ':' + date.getMinutes());

Output:

Thu Jan 02 2025 1:30

Common mistake

Adding a month to January 31 gives March, not the end of February, because February 31 rolls over:

const date = new Date(2025, 0, 31);
date.setMonth(date.getMonth() + 1);
 
console.log(date.toDateString());

Output:

Mon Mar 03 2025

Thanks for reading!

Short answer

Without changing the original

Months and years

Hours and minutes

Common mistake

Functions used in this recipe

Thanks for reading!