Once your Japan Rail Pass has been activated, you can no longer change the selected days. When you swap your Exchange Order for the actual Japan Rail Pass you are asked to select the day you want to start using the pass. This day is referred to as the 'activation date'.

In 2026, the rules for changing your Japan Rail (JR) Pass activation date depend on whether the pass has been physically issued yet. If you have an "Exchange Order" (the voucher you receive before arriving in Japan), the activation date is not set until you go to a JR Exchange Office in person. At that moment, you can choose any start date within 30 days of the exchange. However, once the physical JR Pass has been issued and an activation date has been printed on it, it is generally impossible to change. The only exception is if you return to the exchange office before the start date begins; they may be able to cancel and re-issue the pass for a fee (usually around 10–15% of the pass price), provided it has not been used. Once the start date has actually arrived or passed, no changes or refunds are allowed. If you purchased your pass through the official "JR-West" or "JR-East" websites, you may have slightly more flexibility to adjust the start date online before your arrival, but once you collect the physical ticket at a kiosk or counter, the date is locked in.