Is it possible to become a buddhist without a formal teacher?

The question is not how to become a buddhist; the aim is to get freed from our misery (dukkha). This is possible through realizing wisdom (panna).

Everyone can become enlightened. The Buddha has given us the tools; showed us the path, but everyone has to cultivate it himself or herself.

Ajahn Jayasaro (* Mindfulness, Precepts and Crashing in the Same Car p. 33-35 emphasized text*):

'The Buddha says we can find an inner refuge in which we become like an island unto ourselves, like a mountain which is unmoved by wind and rain and weather. This kind of stability and integrity of mind 'is not found by turning our backs on certain experiences and trying to create some special blissed-out state. If you practice meditation because you’re fed up with life, or you’re fed up with yourself, and you just want to go somewhere else where you don’t have to put up with all this stuff, then you’re already on the wrong path. That is the practice that may lead to heaven. But it’s not the practice for liberation.

You might be able to enter some heavenly realm where you can just close your eyes and feel good for a while, but the ability to do that is conditioned by health, by external circumstances and so on, and it’s not something we can ultimately rely upon. The immediate understanding of things as they are, of highs as highs, lows as lows, thoughts as thoughts, perceptions as perceptions, this is where the stability comes. We begin to see things less as solid entities, we perceive less in terms of personalities and people, and more and more in terms of a stream, a conditioned flow of phenomena.'

I would say that technically you could practice Buddhism without a teacher perhaps learning from book, blogs, videos etc... However from my own experience this didn't work very well. You will bring a lot of thoughts, opinions, stories and generally life baggage to your practice and your really need someone to help you sort this out. That might be a teacher or the sangha that grows up around a teacher.

From my own perspective I couldn't tell the difference between nihilism and Buddhism and this unnecessarily held me back. I trace this back to my own atheist background baggage. Conversely I know people with Christian backgrounds who struggled with perceived notions of sin in Buddhism and people with difficult family background who struggle with perceptions of purity. But whatever your background I would contend that a little help from your your (spiritual) teacher and friends would be a huge benefit.

Buddha is only teacher of All Buddhist. But in this present lifestyle,timeless busy people need guidence, so Buddhist monk could help us, n useful here. Karuna,Shila,Metta are the pillers of Buddhism, so accept the pancashila in your day to day life, which helps a person to become a buddhist. It is not a Damma, Lord Buddha never produce any damma, he guided us a new way of lifestyle, which help us to enlightened inside.

Yes, you can become a Buddhist without a formal teacher or formal training. I would recommend real, paper, dead-tree books as opposed to online research. Books on Buddhism tend to be of higher quality than some of the stuff you find online.

Eventually, however, I would encourage you to visit a monk (bhikkhu or bhikshu) or a nun (bhikkhuni or bhikshuni) at a temple.

I practiced Buddhism on my own for several years before I met any other Buddhists.

The Buddha found the reality pertaining to our misery and the way out of it.

Anybody giving fair trial to the Buddha's practice or eradicating misery for one self can be considered a practising Buddhist. Some level of devotional acceptance of the teaching and the Sangha can also be considered Buddhists.

So most importantly is to develops some faith in the techniques and consider it your teacher and guide (without some faith you will not give it fair trial) then putting it to practice is the most important aspect off becoming a practising Buddhist.

It depends on what you mean "true" Buddhist. If you mean sincere, devoted, mindful and so on then of course.

Can you be enlightened? Yeah I think people say that, but only super super SUPER rarely!

I think a better question is why you feel the need to become a Buddhist. Self identification is just another form of attachment. Why not just practice Buddhism and be done with it? :-)

I started practicing Buddhism as a self-taught curious kid. And I got really into it when I found out that I had not to be affiliated to a certain institution: I had only to apply some concepts to my life and seek to make good.

IMHO you don't need to have a master/teacher to learn what Buddhism is really about, aside from its branches, and to start practicing it. But a teacher is really valuable, because we normally feel like sharing this experience to others, and because it is really hard to supress our ego.

The teacher will be there to share his experience but also listen. He will also be a constant reminder that we know too little and that we think too much.

I find it very nice to find others that follow Buddhism practices and to listen from their unique view and experience.

First of all, there isn't one agreed upon definition about when you are truly a Buddhist

This is wrong! The agreed upon definition is that when you take the triple refuge you are considered a Buddhist. Yes, it is possible to become a Buddhist without a formal teacher as long as you understand taking refuge in the Triple gem. After that, the Buddha, the Dhamma and the Sangha are your teachers.

Here are five ways to take refuge in the Triple Gem as per the Visuddhimagga: