How Accurate Is Google Keyword Planner

When OP says "accurate" what does he mean? Accurate in terms of reasonable and related keywords... yes. Are the numbers always in line what your results are, of course not. But I don't think there is a better resource, paid or otherwise.

-ThopHayt

If you are looking for organic search volume then Keyword planner is not 100% accurate because its provide paid search data

In terms of the searches that their search engine gets daily, yes, it is very accurate in that aspect - please note that there is a large bulk of search engine searchers who would search for a keyword, and does nothing about it, and that's about it.
In terms of how well a particular keyword would convert or would potentially visit your website, then the G keyword planner tool isn't accurate at all. The only best way would be to spend your money on the keyword, and gauge the conversion ratio to see whether that keyword is profitable or not.
Then there's also a serial result clicker as well - they would click on your ads, go into your site, and does nothing. You lose money, your ratio is affected, and they do not contribute to your revenue in the process.

The data is accurate, dont forget combine it with google trends, and for each matrix (search manualy from google search)
You will not need any kw tool if you can combine it.

GetMoreFans said:

After testing it tons of times in tons of different niches - It's not. In most cases, there is MORE TRAFFIC than what the keywords planner shows, so it's a "good" mistake for our favor lol

Click to expand...

Yes the shown data is a couple of months back.

It's 100% accurate and better tool to know the keyword searches and local keyword data. Try out yourself if you don't believe.