IQ test quality
Free IQ test
On the Internet you can find numerous free IQ tests. It must be said that with only few exceptions, free tests will not give reliable IQ measurements. They can be very useful as exercise material and in preparation for e.g. an assessment, but do not expect to see your real IQ score.
Standardization - comparison or norm group
In addition, some of the tests offered on the Internet compare your performance with a non-representative group of others. While it can be fun to be compared with Greeks, or with a random group of people (for instance everybody that has already taken the test), it will not result in a relevant IQ score. Often you will achieve a very high score, just to make you feel good about yourself.
Professional IQ tests
Professional IQ tests, like the ones used in official psychological research and in education, are much more reliable. Unfortunately, most of those tests worldwide are out-of-date. That means that your performance is being compared with a group of others who took the test up to 20! years ago. That results in a substantial overestimation of your IQ.
Besides, being tested by a psychologist is usually very expensive.
Free valid IQ tests
There are only few tests that meet all the above conditions and still are affordable. There are hardly any sites that offer decent IQ tests for free. Keep in mind that generally you will be compared with a group of non representative others. That means that the IQ score may not be relevant.
In addition, free IQ tests tend to ask for a lot of background information.Of course, you could consult with a psychologist. That is a lot more expensive and you should always ask for the 'age' of the comparison group that is used to determine your IQ.