Pray they will accept you. Hell, there is no big issue here. Not believing in god is not a sin as you do not believe in godly sin also. Just state your thoughts and move on. To be an atheist, we must realize that the religious group are not what they preach , rather they will most likely condemn you. And then you move on once again.

Write it all in a song and sing it to them. (Just kidding). I'd suggest a simple explanation, and then suggest to them that you would be willing to answer any questions that they have. They might not care about every single last detail, but they'll probably want a few bits of clarity. Let them choose the topics for you to explain.

Hi JrDuke01,I think you should do the latter part explain why you aquired the disbelief in god.or why not question your parents when the opportunity arisebelief in a god.

I would like to add (as Sam Harris pointed out) that everyone knows what it's like to be an atheist. I used to have a Facebook group (when I had a Facebook) called the Plus Ones. It was a statement about how a theist denies the existence of thousands of gods that have been worshiped throughout recorded human history, and I deny the existence of all of those same gods, plus one.

You could try something along this line:

I came out to my parents at Thanksgiving. I said, “Mom, please pass the gravy to a homosexual.” She passed it to my father. A terrible scene followed.
~ Bob Smith—Gay Comic

As a gay agnostic, I can assure you, it's best to just say it. Maybe let them know you'd like to have a sit-down, and then tell them what you need to tell them. Just the facts at this point. They're probably not going to care about the logic of how you got there right now. Over time, though, they'll probably start asking questions.

That's why I posted the above quote. It's hilarious, AND, it accomplished what it was meant to accomplish without being unnecessarily harsh.

I think you acquired knowledge in science and disbelief just came about naturally, then. I fought it for years - actually saying I am atheist, because I was so inculcated with my Christian heritage belief system.
But, it finally just became too much. I couldn't say those creeds in church anymore. The anthems made me want to throw up - so bloody and cruel. The sermons didn't make any kind of sense. Everything was evil, cruel, mean and harsh...and supposed to represent a loving Father. I got really tired of feeling guilty for making Christ have to die on the cross for me when I still might go to hell. It just didn't make sense. I gave up the fight and have been so happy ever since.

I think I need to post it here as well. (I seem to be having to explain this almost every day.) Atheism and Agnosticism are not two different points on the same scale. (i.e. Agnosticism isn't Atheism light.) They deal with completely different things. Agnosticism deals with that which one can know and Atheism deals with that which one believes. I am an Agnostic Atheist because I don't believe in god, but I know that no one can know whether or not one exists. I have met a few self-described Agnostic Christians, even though technically, every single theist out there should consider themselves an agnostic theist.

There are a ton of ways to go about this, and we all have stories. If you can narrow down what you're looking to accomplish and a little about your family dynamics, we may be able to offer better advice.

Why do you have to say anything at all? You don't owe them an explanation...it's your life.

Be blunt and tell them. Let them go through the stages of coming to terms with the fact.

Many of the posts here cover "why tell them at all?", so I'll respond with "how do I tell them slowly?"

First, only tell the truth, just not all of it at once.

Start with saying you no longer believe what that church teaches (you don't have to add that you don't believe what ANY church teaches). Then say you are looking for your own truth. Then when people are still asking and are open-mindedly listening, you can tell them what you've decided the truth to be for you. Make sure they understand it's about you and that their beliefs are up to them. The arguments usually stem from "how dare you not believe in MY god!".

It is a private matter, as all belief systems should be....why would you need to make some big announcement about it?

just get to the point and let them ask the questions

I don't know how much you have had a chance to read or watch videos from your new community. There is a lot of wonderful stuff out there. They can be useful two ways, as you more fully explore the world view you will be more eloquent in answering their questions and be more confident to do so.

Also, there is much you might share with them directly.

One of the hardest things to get them to understand that it isn't a bleak worldview at all.

Here's one -

Have you read Demon Haunted World?

I've got a mountain of likely suggestions if you're interested.

After moving out I told them I was atheist, they were scared because I had never shown any “signs”, like it was a mental illness. One day my Dads invited me for a walk and asked me if I believed in angels, I said no of course, he followed up by asking if I believed in demons. I had to explain to him that I’m not evil now that I don’t believe the lies iv grown up with, and that whatever they believe is fine as long as it stays in the afterlife, because right now only what I can know will matter to me. Don’t ask me to participate in rituals, like prayer before meals, enjoy on your own, I’ll poor drinks. I’m glad my parents try to do what’s right, maybe in the future they can be saved from their lies.

A simple declarative sentence ought to do it. It's just like saying, "my eyes are green".
Their reactions are out of your control. Live your own life to your own satisfaction.
You can't make anyone "understand" anything.

You're an adult. Do you live with your family? Do you want to move out? Are you employed and prepared to move out? You have to take one step at a time. Weigh the options. Then tell them you are an atheist. Best of luck and welcome you have friends here.

Well, it's different for everyone but I would start by just saying it out loud somehow. They ask you to pray or mention something religious to you that you don't want to do or disagree with, it makes it more natural to say "I don't believe/(want to do) that because I am an atheist."

Then likely questions come up from them that you can hopefully calmly answer, or bluntly if you have to be more assertive.

Best case is they say "Ok" and it ends there (my experience with members in my family) they acknowledged I don't believe what they do and we openly discuss our stances or why we do what we do.

Worst case they stop talking to you, try passive aggression or actual violence, where the law will protect you, in which case that's more their issue then yours, it may be a problem if you're living at home or lose doing things you enjoy doing with them but ultimately if they can't accept you then that's no family.

This is almost impossible to answer, I have a friend whom is gay and an atheist. His family accepted that he is gay but he had to move to where he was safe (from the bible belt to California) because he is an Atheist.
For me it was easy, after my wife's head exploded and caused a small earthquake she deals with it as long as I'm not "an activist" locally. Thus here I am. In live in Colorado and have had little push back, I have even befriended the most, very most unlikely of people....(clergy).
I am care full to "share" my thoughts. "I just couldn't believe there was a talking snake." I did not attack anyone's belief or religion. I simply "shared" my doubts. With this technique there is no debate and the listener might actually not only "share" your thoughts(even though they don't have to admit it) but it's difficult to debate about your doubts, they are yours....and it just might plant a seed of thought for them to work out on their own.