The Tokyo Olympic Games will start on 23 July, 2021 and will run to 8 August after it was postponed for a year because of the coronavirus pandemic.
The executive board met on Monday to make a decision after the 2020 Games were moved from this summer.
The Olympics will still be called Tokyo 2020 despite taking place in 2021.
The Paralympic Games, origianally due to start on 25 August, 2020, will now take place between 24 August and 5 September, 2021.