Customer Service Number

Your CSN is your key to unlocking the many secure online services offered by the Franchise Tax Board. A CSN is a 4-digit authentication number California issues. A new Customer Service Number is issued to every taxpayer each calendar year. The number is only valid during the year for which it is assigned. The combination of the CSN and the taxpayer's social security number ensures confidentiality and security when conducting business electronically.

With your social security number and CSN, you can:

E-file your return.
Check your account balance due.
View payments you've made.
Make tax payments online.
Apply for an installment agreement.

You can obtain your CSN the following ways:

By mail - If you e-filed your own return last year, we sent you a sealed postcard with your CSN inside.

On the CA Website - If you didn't receive your CSN in the mail or if you lost it, you can look it up online at http://www.ftb.ca.gov/online/csn/

You will not be able to complete electronic business transactions with us if you use a wrong CSN. You must use the CSN that California has assigned to you.

Generally, you will not be able to change your CSN. However, if you have a circumstance that requires a new CSN be issued, please contact the California Francise Tax Board.

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