put two and two together and get/make five

to guess something wrong about a situation, usually something more exciting than the truth.

She thought I was pregnant. I was sick a couple of times and she just put two and two together and made five.

• ply with something
• ply your trade
• poacher turned gamekeeper
• poetic justice
• poetic license
• po-faced
• point-blank
• point blank
• point of no return
• a babe in the woods
• a baby boomer
• a back-handed compliment
• a backroom boy
• a backseat driver
• a bad apple
• a bad egg
• a bad workman blames his tools.
• a bag lady
• a bag of bones
• a baker's dozen
• a balancing act
• a ball and chain
• a ball-breaker
• a ballpark estimate
• a ballpark figure