theta is always negative for long calls and long put

[qin841121]

This is a statement by schweser and also investopedia. How can it be true?

For long put, the longer the option, the cheaper it may get as the expected price of stock will be higher due to interest and because of this the put will decrease in value?

What is wrong with my logic?

 

[Jas]

Theta for a long call is always negative. True.

However, Theta of a long put always exceeds the theta of a call by a fixed amount. Hence for out-of-money puts, the theta may be positive also.

Another concept to be aware of, theta is measured in terms of "time remaining to maturity (T-t)" in contrast to "time passed (t)" - thinking in terms of "time passed" may be akin to reversing the sign of theta.