It's similar to colourblindness, in that it's really hard to tell because it's all you've ever known. Your best bet is probably to try an online test and go to see a doctor if it suggests there could be something there.

This one looks good: https://www.additudemag.com/adhd-symptoms-test-adults/

Like the other reply mentions - it's quite hard to tell. I've long had a feeling there's something wrong in me. The other week I ran into an ADD-test (https://totallyadd.com/do-i-have-add/) and gave it a try. I got 17/18. After some research and long discussions with my wife I contacted a doctor who after discussing with me sent me to see a psychologist.

> How do you know you have ADHD?

That is best found out by a multi-angle approach including brain images, intelligence tests, patient history, family history, etc...

Seeing a doctor is critical because a) it is easy to misdiagnose oneself and b) there are some problems that lead to similar symptoms as AD(H)D, i.e. bipolar, problems with your thyroid gland, vitamin deficit, trauma and so on, so it is also important to exclude these.