No online IQ test will come close in terms of quality.

There is, however, for every test, something known as a “floor effect” and a “ceiling effect”. For example, on the Wechsler Adult Intelligenced Scale (one of the most highly regarded IQ tests), a score of zero wil give you an IQ of around 40 or 50, depending on your age. This led to a humorous artice entitled “Assessment of the Dead”, as even a corpse that “failed” every question (due to nonresponsiveness) would get an IQ score in this range.

Similarly, there is an upper limit to the score you can achieve on an IQ test, and, because of the way the Bell Curve works, at the upper end of an IQ test, a difference of a few correct items makes virtually no difference on the IQ.

These problems exist for any IQ test, but online tests should be viewed with particular suspicion, as they are unlikely to be well-constructed.

If you want to know your IQ with any degree of accuracy, be prepared to spend $1500-$2000 for a psychological assessment. Having said that, when someone does a proper psychological assessment, the final IQ score is really almost irrelevant. Psychologists are more interested in the subjects pattern of performance on the IQ test and what that can say for helping the person to be more successful in school, work, and life.