SSA in the United States offers a simple and effective piece of advice for many Americans. The Social Security number is more important than it seems, and the government clearly explains why it's not a good idea to overlook it.
SSA recommends applying for the Social Security number before leaving the hospital, right when requesting the baby's birth certificate. When you fill out the information for the birth certificate, the staff will ask if you want to request the baby's number. It's the easiest way.
If you have a baby in the United States, SSA advises you to do this soon
You can do it as soon as the baby is born. In fact, the hospital is the most convenient and efficient place to do it. If for some reason you don't request it there, you can still do it online through the SSA website and complete the process at an office or card center.

The best time is at the moment of birth, during the birth certificate application, before leaving the hospital. At this point, everything is processed together, with no waiting or duplicate procedures.
Why not wait to get the Social Security number?
Avoid delays: if you wait and go to an SSA office, you'll have to wait for the birth certificate to be verified, which can take weeks. Doing it at the hospital is convenient, fast, and lets you focus on the baby, without paperwork later. In addition, the baby will need it for tax returns, a bank account, medical coverage, or savings bonuses.
SSA explains that, once the state reports the birth (usually in about 9 weeks), they send the number and card in about 10 more days. In total, it could take about 4 to 6 weeks from birth to receive the card at home. Times vary by state, but the average is two weeks after the state notification.
Steps to take: SSA is clear and direct
At the hospital, fill in the baby's information for the birth certificate. When asked, indicate that you do want the SSA number and provide both parents' SSNs. The hospital sends the information to the state and then to SSA.

Wait for the card to arrive by mail at your home. If you don't receive it, call 1‑800‑772‑1213 or go to an office. If you do it later at an office or online, you'll need the birth certificate or proof of birth and citizenship.
You'll also need the baby's identification document (such as a vaccination card or passport) and your SSA identity. If you apply at the hospital, SSA uses the documents already submitted for the certificate, avoiding additional procedures.