National Insurance (NI) is paid by individuals and businesses to HMRC. NI contributions are paid to qualify individuals for state pension and other benefits. There are several types of national insurance, known as class 1, class 2, class 3 and class 4. The class you pay will depend on your circumstances. For example, an employed individual may pay class 1, whereas a self-employed individual may pay class 2 and 4. Class 3 are voluntary contributions and are usually paid to fill any NI gaps to ensure an individual qualifies for a full state pension.