Way to transfer or copy field contents to another field in the same module upon input?

Way to transfer or copy field contents to another field in the same module upon input?

For instance, I have a custom text field titled "estimate" and another field titled "Latest." I would like "latest" to update with whatever I put in "estimate." 

If I put down Estimate = 900, I wish to have 900 automatically entered on the "Latest" field as well.