Summarize this article:

A tube of whitening toothpaste typically costs less than $10 at the drugstore or local supermarket. ADA-approved whitening toothpastes use abrasive particles to polish teeth along with chemicals that bind to stains and remove them. Studies have proven that these toothpastes are no harder on your enamel than other toothpastes. Blue covarine binds to your teeth and creates an optical illusion that makes them appear less yellow. You should see some results within two to four weeks. For increased effectiveness, follow up with whitening mouthwash.

Summary:
Use whitening toothpaste if you're on a tight budget. Look for a toothpaste with the American Dental Association (ADA) seal of approval. Look for an ingredient called blue covarine in your whitening toothpaste. Brush twice per day.