- Calvin once made Susie a valentine and flowers (albeit a hate-mail valentine and dead flowers, but it showed he cared).
- In that same story arc, Calvin was left thinking "She noticed! She likes me!".
- In one Sunday strip, Calvin and Susie exchange insults, and Calvin says "It's shameless the way we flirt".
- Calvin's good side began writing romantic love poems to Susie and offering to carry her books for her and sent her flowers. As it is a projection of Calvin's good side, and therefore, is half of him, this practically confirms Calvin's love for Susie.
- In one strip when Hobbes was stolen by a big dog, when Calvin found out that Susie had Hobbes, he kissed her hand, but Hobbes stole her cookies.
- Calvin sits with Susie during lunch.
- When Calvin calls Susie a "booger-brain" and makes her cry, he genuinely feels bad and is upset when she initially ignores his attempt to apologize.
- Once when he did not sign up for baseball he played with Susie in the swings.
- Sometimes he sits next to her on the bus stop, and in the bus.
- When she received the hate-mail valentine and dead flowers from Calvin, she thought "A valentine and flowers! He likes me!"
- In the story arc with the last meeting of G.R.O.S.S., Susie raced to the hall closet, believing Calvin to be trapped in it.
- When Calvin calls asking about homework, she tries to make him say he "missed the melodious sound of her voice".
- She invited Calvin to her birthday party.
- Although she is grossed out by Calvin's eating habits, she still sits with him during lunch.
- A popular fan theory is that Calvin and Susie end up getting married as adults and have children of their own.
- In The Calvin and Hobbes Tenth Anniversary Book, Bill Watterson states "I suspect Calvin has a mild crush on [Susie] that he expresses by trying to annoy her, but Susie is a bit unnerved and put off by Calvin's weirdness. This encourages Calvin to be even weirder, so it's a good dynamic."
- Confirmed by Watterson, Calvin and Susie do like each other.
They married and had a kid named Bacon in a fan comic called "Hobbes and Bacon".