When to change transmission fluid?

Add fluid now. First, get the engine hot and then turn it off for 5 minutes. Then check level three times. Transmission fluid is sometimes real hard to see on a dipstick. You can add too much and ruin it but if it's not above the cross hatched lines you are ok. Have the transmission flushed every 25 to 30 thousand miles. Something that people rarely do unless you want to save the cost of a new .