resulting reports must be presented to the UK Parliament. The most recent review was conducted as at April 2015, with the report being published two years later. Contributions The contributions component of the system, "National Insurance Contributions" (NICs) are paid by employees and employers on earnings, and by employers on certain benefits-in-kind provided to employees. The self-employed contribute partly by a fixed weekly or monthly payment, and partly on a percentage of net profits above a certain threshold. Individuals may also make voluntary contributions, in order to fill a gap in their contributions record and thus protect their entitlement to benefits. Contributions are collected by HM Revenue and Customs (HMRC) through the PAYE system, along with Income Tax and repayments of Student Loans and Postgraduate Loans. People in certain circumstances, such as caring for a child, caring for a severely disabled person for more than 20 hours a week or claiming unemployment or sickness benefits, gain National Insurance credits which protects their rights to various benefits. National Insurance is a significant contributor to UK government revenues, with contributions estimated to comprise 18% of total revenue in the 2019/2020 financial year. Contribution classes National insurance contributions (NICs) fall into a number of classes. Class 1, 2 and 3 NICs paid are credited to an individual's NI account, which determines eligibility for certain benefits - including the state pension. Class 1A, 1B and 4 NIC do not count towards benefit entitlements but must still be paid if due. Class 1 Class 1 contributions are paid by employers and their employees. In law, the employee contribution is referred to as the 'primary' contribution and the employer contribution as the 'secondary', but they are usually referred to simply as employee and employer contributions. The employee contribution is deducted from gross wages by the employer, with no action required by the employee. The employer then adds in their own contribution and remits the total to HMRC along with income tax and other statutory deductions. Contributions for employees are calculated on a periodic basis, usually weekly or monthly depending on how the employee is paid, with no reference to earnings in previous periods. Those for company directors are calculated on an annual basis, to ensure that the correct level of NICs are collected regardless of how often the director chooses to be paid. There are a number of milestone figures which determine the rate of NICs