Where do atheists get their morality from?

[Red Celt]

How do atheists know what is morally right or morally wrong? Is morality cultural, gut feel, are there any basic principled you can use? Opinions?

The Golden Rule predates religious morality. It has been used by social animals (including man) for thousands of years.

Tsze-kung asked, saying, "Is there one word which may serve as a rule of
practice for all one's life?" The Master said, "Is not Reciprocity such a
word? What you do not want done to yourself, do not do to others."

— Confucius, Analects XV.24