Why is error message saying input is not a returning string

I'm trying to make a hangman game. I want to check if the user's guess of a letter is in the word but I'm getting an error saying

TypeError: 'in <string>' requires string as left operand, not builtin_function_or_method

I'm not sure what I'm doing wrong as I thought 'input' should always return a string unless otherwise stated.

Here's my code:

def pick_word():

word = random.choice(words)

for letter in range(len(word)):
    print("_ ", end = '')
    print(word)

guess = input("\n \n Guess a letter: ").lower

if guess in word:
    print("Well done!")
else:
    print("{} isn't in this word. Try again.".format(guess))

Thanks for your time! :)