You lose reputation when:

• your question is voted down: −2
• your answer is voted down: −2
• your article is downvoted: -2
• you vote down an answer: −1
• you downvote an article: -1
• you place a bounty on a question: − full bounty amount
• one of your posts receives 6 spam or offensive flags: −100

All users start with one reputation point, and reputation can never drop below 1. Accepting your own answer does not increase your reputation. Deleted posts do not affect reputation, for voters, authors or anyone else involved, in most cases. If a user reverses a vote, the corresponding reputation loss or gain will be reversed as well. Vote reversal as a result of voting fraud will also return lost or gained reputation.