Contribution rates vary for all TK policy holders, depending on medical factors, their age, and their personal income
The basic contribution rate for TK customers is 15.3% of income. 0.7% of that forms a supplementary rate for TK customers.
The "general contribution" as required by German law is 14.6%, half of which is paid by employers. So employees should have to pay a minimum of 8%.
However, there are some variations. Self-employed individuals pay a reduced basic rate of 14%, so their contribution will add up to 7.7% with the TK supplementary contribution included.
Retired individuals also use the same system, but instead of an employer covering half of their insurance costs, the German state covers half of the bill.
Additionally, all TK insurance customers must pay a Pflegeversicherung (nursing contribution). This is always smaller than your monthly health insurance contribution, and varies depending on whether individuals have children. It's used by the state to fund long term care, generally for the elderly, and is also shared between employers and employees.
How to calculate your contribution rate
Questions range from your monthly income, to whether you have dependents, or how old you are. The whole process takes a minute or two to complee, and creates an easy to understand visualization of expected insurance costs (including the care charge).
However, it's not final. Insurance costs can be influenced by whether individuals have secondary income sources, such as rent, extra self-employment income, or pensions. Still, it's a good starting point.