What to Write in a National Sibling Day Card

Siblings: they know all your secrets, all your embarrassing stories, and probably have blackmail material from the 90s. But they’re also the people who’ve been there through every weird family holiday, broken toy, and shared bag of crisps. National Sibling Day is your chance to show them a little love—or give them a gentle roast. Either way, a card is the perfect place to say it.

Whether you’re all about the mushy stuff or prefer a message that says “I tolerate you,” here are some ideas to help you nail the perfect National Sibling Day card.

From day one, you’ve been my sidekick, rival, and ride-or-die. Thanks for surviving childhood with me.

We share parents, secrets, and way too many embarrassing stories. Wouldn’t trade it for anything.

Sweet & Sentimental

Sometimes, siblings really are the best—built-in best friends who’ve been there through every milestone, meltdown, and moment that mattered. If you’re feeling all the feels, these messages will help you express your gratitude and affection without getting too soppy.

Thanks for being my built-in best friend.
I don’t say it enough, but I’m really lucky to have you.
Through every high and low, you’ve always been there. And I’m so grateful.

Remember when we tried to kill each other over the TV remote? Good times.

You’re the only one who truly gets the chaos we grew up in. Therapy buddies forever.

Funny & Relatable

Because no one gets your sense of humour quite like a sibling. These messages are for the ones who understand your sarcasm, remember your most embarrassing moments, and will absolutely remind you of them.

We may not have chosen each other, but we’re stuck with each other. Happy Sibling Day!
Congrats on having the best sibling ever. You’re welcome.
Remember when we used to fight over the TV remote? I won. Just saying.

Appreciate you taking the blame all those times. Teamwork makes the parents less mad.

You stole my stuff, mocked my music, and somehow still became my favourite person.

Childhood Flashbacks

The shared chaos of growing up together creates some of the best memories. Use your card to throw it back to the moments only the two of you remember—and maybe laugh at now (instead of cry).

From blanket forts to awkward family holidays—you made it all better.
You’ve always been the peanut butter to my jelly (or the chaos to my calm).
Remember when we convinced Mum to let us eat ice cream for breakfast? Peak teamwork.

If I roast you, it means I love you. Don’t get used to compliments.

It’s fine, you were the favourite child… but I’m clearly the funniest.

For Siblings Who Are Like Best Friends

Some siblings are more than family—they're your go-to person, your emergency contact, and your built-in therapist. If you’re basically inseparable, these messages say it all.

You’re not just my sibling—you’re my favourite human.
Life’s way more fun with you in it.
Thanks for being the one person who truly gets my weird.

Playful Roasts (With Love)

Let’s be honest: teasing is 90% of a sibling relationship. If you show affection by throwing shade, these tongue-in-cheek messages are perfect for keeping the love alive—with just a touch of mockery.

You’re my least annoying sibling. And yes, I’m counting myself.
Still shocked you turned out halfway decent.
You might be older, but I’m clearly the favourite.

Okay, maybe I would’ve swapped you once or twice… but only for better snacks.

We’ve got years of jokes, grudges, and memories. Wouldn’t have it any other way.

Creative Add-On Ideas

Want to give your card that extra spark? These personal touches add a layer of fun (or embarrassment) your sibling will totally appreciate—or pretend not to.

Include a childhood photo that’ll make them laugh (or cringe).
Add a silly doodle or your best attempt at a meme.
Create a "Sibling Survival Kit" with snacks, bandaids, and earplugs.

Say It Your Way

Whether your card is sweet, sarcastic, or somewhere in between, it’s a fun way to celebrate the weird and wonderful bond that only siblings understand.

Want to show your sibling some love (or stir the pot just a little)? Check out our greetings cards for brothers and sisters, and say it your way!