After you have successfully joined the Google Adsense program, the next target for most of us is to reach the payment threshold 100$. When I started blogging and joined Adsense back in 2008, this was the question I asked in so many places on the internet. But I couldn’t find correct answer. Even now, it is difficult to predict and confirm the formula to make your first 100 dollars from Adsense. Because the earning from Adsense is completely different for every blog, topic, traffic source and country of the visitors. I have decided to put a simple formula which may give some ideas to understand how long you may take to earn your first 100 dollars.
UPDATE: I’m updating this post almost after 4 years with the learned lessons and the experience.
Below was the my first check from Google Adsense which took quite long time.
Ok, Lets go to the point. This is just an average calculation with assumption. None of the Adsense publishers are allowed to publish their details stats like RPM, CPC and CTR publicly which is against Google Adsense TOS.
There are three important factors involved in our below calculation which are CTR ( Click Through Rate), Page CPM( Cost Per Mile). RPM is new factor ( Revenue Per Mile), but we are not going to talk about it here. Each factor directly impact the final Adsense Earnings.  We are not considering CTR in this calculation, but I can say if you can increase your current CTR rate, that will boost the final earnings.
So, its all with CPM we are going to take here. Adsense CPM indicates how much you earn from every 1000 page impressions with Adsense ads (no matter how many ads on them)
So, if you earn 5$ from 2500 page impressions, your CPM is,
(5/2500)*1000 = 2$
You earn 2$ from every 1000 impressions.

How Longs Takes to Earn First 100 Dollars From Google Adsense

Here is the point, I can’t tell how much is the best CPM, it completely depends on your blog niche and traffic source.
In my experience and what I read from other blogs, 1.5$ to 2.5$ will be an ordinary CPM currently.
If its less than 1$, then you should improve and concentrate on increasing Google adsense income.
If you are getting around 3$ to 5$ CPM continuously every month, then you doing well, if it is more than 5$, then it is a great CPM rate.
In our case, we will take 2.5$ as average eCPM and to make the calculation easy, we will do it for first 105 dollars.
So, with 2.5$ eCPM to earn 105 dollars, you need 42,000 page impressions.
(1000/2.5)*105 = 42,000
This figure can be less or more for you, because it depends on type visitors, source of traffic and country of origin which make these impressions.
So, lets go to the next step.
When a visitor visits your blog, he or she checks average 1.5 pages on a blog.
To get 42,000 page impressions, you need 28,000 visitors.
(1/1.5) * 70,000 = 28,000
Again, this 28,000 visitors can be from direct, referral, social networking and search engines sources.
Mostly the search engine traffic users (who come from Google, Bing and Yahoo search) will be useful for any CPC programs including Google adsense. Because they are the new users and will possibly click the ads on your website. Your regular visitors and social networking users may not be interested on the ads showing up in your blog.
65% to 75% search engine traffic will be healthy for a blog in my opinion. In this example, we will take 70%.
So, in 28,000 visitors, you need 70% of organic traffic, which is 19,600 visitors
(70/100)*28,000 = 19,600 visitors from Search Engines

Wow, that’s a big number.

Now you can get rough idea based on your average CPM (Also called RPM) and daily search engine traffic to know when you will get the first 100 dollar adsense check.
I have updated few numbers and CPM rates now (compared to previous version of this guide in 2010). Because in my opinion, the potentially of making more money from Google Adsnese has been improved since 2010. There are lot of competitions and bidding among advertisers in Google Adwords market place. That enables bloggers like us to get higher earnings because of higer CPC ( Cost per Click).
If you are getting 100 average daily search engine traffic visitors, then it may take around 6 to 7 months to get your first 100 dollar from adsense.
But one thing, Your blog will not be getting the same 100 daily search engine visitors for next 6 months, it will increase when you update your blog with unique content regularly. So, once you blog properly with correct techniques, then you can reach 19,600 search engine visitors quickly and get your 100 dollars.
Finally, it all depended on your adsense optimization to get high CTR, CPC and CPM, organic traffic and keyword selection. But to know these techniques, it will take some time for new bloggers.
If you think this calculation is wrong, feel free to share the reason. Still if somebody is not making any money from adsense after this much traffic, the contact me. I will try to help you.