According to the U.S. Passport Service Guide, you can renew your passport whenever you want if you have good reason to do so. You should include a letter explaining the motive for the request along with the renewal application if it is submitted more than 9 months prior to the expiration date.
Application for a passport renewal should be done approximately nine months prior to the passport's expiration date. There are three reasons for renewing your passport so early. One, the earlier you apply, the less likely you are to need expedited services. Expediting a passport can be quite expensive.
If you meet certain criteria, you may be able to renew your passport by mail using Form DS-82.
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