How long is my Eurail Pass valid?

That depends on your Pass. If you already have a Pass, the expiration date is at the top of your Pass. That's the last day your Pass is valid, and you can use it until midnight.

Don't have a Pass yet? If you know which Pass you want, you can easily calculate how long it will be valid:

For Passes that are valid for a specific number of travel days within 1 or 2 months, your Pass is valid for 1 or 2 months from your start date. During this one or two-month period, you can use your travel days at any time.
For example, if your start date is January 10th, and you have a Pass for 7 days within 1 month, your Pass is valid from January 10th to February 9th. The Pass expires on February 10th.
For Continuous Passes that are valid for 1, 2, or 3 months, your Pass is valid for 1, 2, or 3 months from the start date. During this period, you can travel every day with your Pass.
For example, if your start date is July 4th, and you have a 3-month Pass, your Pass is valid from July 4th to October 3rd. The Pass expires on October 4th.
For Passes that are valid for 15 or 22 days, your Pass is valid for the specified number of days from the start date. During this period, you can travel every day with your Pass.
For example, if your start date is November 1st, and you have a 15-day Pass, your Pass is valid from November 1st to November 15th. The Pass expires on November 16th.