If I already have an ITIN and then get an SSN, what do I need to do?

Once the Social Security Administration issues you an SSN, you must stop using the ITIN and use the SSN for all future filings. Notify the IRS in writing at the address in the ITIN instructions, sending a letter with your name, mailing address, ITIN, and new SSN, and ask them to merge your prior tax records under the SSN so your history and any credits carry over. Also update your employer, banks, and brokerage so income gets reported under the correct number. An unused ITIN eventually expires. Consolidating avoids duplicate records and mismatched W-2s at tax time. The IRS explains the ITIN-to-SSN transition at irs.gov.