Is the social security card valid until the first or last day of the month?

The last day. The expiration date of the validity period of social security card is the last day of the month, because the validity period of social security card is related to the social security system. In China, the social security system stipulates that social security is paid monthly, so the validity period of social security card is set to the end of the month to ensure that users can enjoy social security rights and interests in a normal and effective payment state.