In Google Analytics for one of the site I am managing, the traffic chart look like this with very consistent monthly cycles. Why does it cycle? I would expect a more linear graph.
Do you publish content at regular intervals?
Without knowing what the site is about, it’s hard to guess. However, cycles like that aren’t all together uncommon.
No, I do not produce content on a regular basis and I have not made any changes to the site during those time. The graph is that of the site LearnWebDesignOnline.com
I’m guessing it has to do Google’s monthly index updates or something. Because 75% of its traffic is from search engines.
Weekends? That kind of shape suggests to me that you’re getting more traffic during the week and then it falls away at the weekend. Depending on your target audience, that could either be exactly what you’d expect or slightly odd. If you’re not targeting business customers, maybe it means that most of your traffic comes from people sneakily making use of their office internet connection when the boss isn’t looking 
Yeah Exactly , The Graph Down when Saturady , Sunday come and Rise on Monday to Friday!!! Thats the main Reason. You should Target more business People .
Not necessarily. If your site is performing well overall then does it matter that the weekends are quiet? Some of the best restaurants in the world are closed at 4am but they are still the best!
Weekends are always a difficult period to target. And considering your site, who would like to study on weekends?..
My website looks exactly the same. We get tens of thousands of visitors during the weekdays, and it dips to around 2k on Saturday and Sunday. It’s a perfectly natural thing if you’re running a serious site, whereas an entertainment site may receive the opposite treatment.
As others have mentioned it is occurring because your niche is one which people mainly use at work, so this is something which is tied to your niche and I don’t think you will be able to change. To confirm this have a look at your traffic around specific holidays and you should see a big dip.
If you can see the graph outlook, you can point-out that there is something happening during the start and end of every month which is causing a dip in the traffic. Moreover, if you check it out more carefully the traffic coming to this particular website has stayed almost same and has not witnessed increase or decrease in traffic. So, please perform some SEO activities which will help the website to increase its traffic flow.
Yeah I know , I Suggested That target Business People!!!