The City of Philadelphia has its own local income taxation system. Philadelphia-based employers are required to withhold the Philadelphia wage tax from the salaries of their employees. Residents of Philadelphia working for an employer are not required to file a local return as long as their Philadelphia wage tax is fully withheld by their employer. If their employer does not withhold the Philadelphia wage tax, residents are required to register with the Revenue Department and file an Earnings Tax return. Residents of Philadelphia with self-employment income are required to file a Net Profits Tax (NPT) return, while those with business income from Philadelphia sources are required to obtain a Commercial Activity License (CAL) and pay the Business Income and Receipts Tax (BIRT) and the NPT. Residents with unearned income (except for interest from checking and savings accounts) are required to file and pay the School Income-tax (SIT).