Sisters are the hardest people to write a birthday message for, and the reason is simple arithmetic. You already send her forty messages a week. The birthday one has to stand out from all of them without turning into a speech, because a paragraph from a sister reads as strange, or worse, as an apology for something. Short is the right instinct. The mistake is assuming short means generic, so people fall back on wishing you health, happiness and everything you deserve, which is what you write to a colleague whose name you had to check. A short wish still has to be a finished thought: one specific thing that is true about the two of you, said in a single breath, then stopped. That is what the lines below do. They run to one or two sentences, they are sorted by who she is to you and how you are sending it, and every one of them is complete as it stands. Take one, change a word if it needs it, send it.
Short birthday wishes to send as a text
Happy birthday. Of everybody I could have been stuck with for life, I am genuinely glad it was you.
It is your day. Do exactly what you feel like and let somebody else handle the rest of it.
Happy birthday to the one person who knows the entire story and stayed anyway.
Another year of you, which is good news for all of us. Have a great one.
Happy birthday. Send me a photo of the cake or I will assume there was no cake.
You get a whole day of being the favourite. Enjoy it. I am taking it back tomorrow.
Happy birthday. I hope today is slow in all the good ways and busy in none of the bad ones.
Wishing you a birthday that feels like a Saturday, even though it is not one.
Happy birthday. You have been my first phone call for years and I have no plans to change that.
Have the best day. You are owed one, and I have been keeping careful track.
Happy birthday. Whatever you were planning to worry about today, postpone it until tomorrow.
One more year of being the person I quietly compare everybody else to. Happy birthday.
Happy birthday. No advice today and no opinions, just this: I am glad you exist.
Short lines for the birthday card
Happy birthday. Thank you for a lifetime of being on my side, including all the times I was clearly wrong.
To my sister, on her birthday: every good thing you wish for other people, all of it back to you.
Happy birthday. You make being related to you both very easy and very lucky.
Wishing you a year that treats you as well as you have always treated everybody else.
Happy birthday. Other people got friends. I got you first, which was a better deal.
To the sister who remembers everything and forgives most of it. Have a wonderful day.
Happy birthday. Here is to another year of being the only two people who understand that story.
Wishing you a birthday full of the things you never get around to giving yourself.
Happy birthday. You have earned one quiet, ridiculous, entirely selfish day. Take it.
To my sister: thank you for the years, the honesty and the endless patience. Happy birthday.
Happy birthday. Growing up beside you is still the best thing that happened to me by accident.
Wishing you a year of good news, arriving in roughly the order you would like to receive it.
Short wishes for an older sister
Happy birthday to the sister who went first and made everything after her easier. I did notice.
You set the standard and then quietly helped me reach it. Happy birthday.
Happy birthday. Half of what I know about doing things properly, I copied directly from you.
To my big sister: thank you for going on ahead and reporting back. Have a wonderful day.
Happy birthday. You have been looking out for me since before I could say your name properly.
You are still the person I phone before I do anything risky. Happy birthday, and thank you.
Happy birthday to the one who took the blame far more often than she ever had to.
Wishing you one day off from being the responsible one. Nobody will notice. Happy birthday.
Happy birthday. You raised me a little too, and you were much too young for the job.
To my older sister: this year, let somebody else organize all of it. Happy birthday.
Happy birthday. I stopped trying to catch up with you years ago and life improved immediately.
Short wishes for a younger sister
Happy birthday to the one who turned up and immediately took over. Best thing that ever happened here.
You were supposed to look up to me, and instead you turned out better. Happy birthday.
Happy birthday, little sister. I still picture you small, and I am aware that this annoys you.
To my younger sister: thank you for never once letting me get away with anything. Have a great day.
Happy birthday. Somewhere along the line you started giving me the advice, and it is good advice.
You have my back now far more than I ever had yours. Happy birthday. I am working on it.
Happy birthday to the sister I taught nothing useful, who then managed brilliantly anyway.
Wishing you a birthday exactly as loud as you want it. Knowing you, that is fairly loud.
Happy birthday. I had a few years head start and you caught up embarrassingly fast.
To the person who has been borrowing my things since she could reach the shelf: happy birthday.
Happy birthday. You grew up into somebody I would have chosen as a friend. Lucky me.
Short wishes when you live in different cities
Happy birthday. Different time zone, same sister, same message every year: I miss you.
Wishing you a great day from much too far away. Save me some cake. Freeze it if you have to.
Happy birthday. The distance has not changed one single thing that actually matters.
I would be there if the flights were kinder. Happy birthday. Call me once the noise dies down.
Happy birthday from the other end of the country. Consider yourself thoroughly hugged.
Another birthday celebrated by phone. One year we will manage the same room. Happy birthday.
Happy birthday. You are the only person I will happily talk to for two hours on a bad connection.
Wishing you a wonderful day. I will be the loud voice on speaker at some point this evening.
Happy birthday. Distance is a detail. You are still the first person I tell everything to.
Have a great birthday. Your present is late and travelling, which is very much on brand for me.
Happy birthday. Same date, different city, entirely unchanged sister. See you sooner than last time.
Funny and short
Happy birthday. You are still older than me for a few more months and I intend to keep counting.
Happy birthday to the sister who taught me how to get out of chores. Still using the method.
Happy birthday. I found you the perfect gift, then panicked and bought you a completely different one.
One year older and still borrowing my things. Happy birthday, and I would like the sweater back.
Happy birthday. As your sister I am contractually obliged to say something nice. You are fine.
Congratulations on another year of being the favourite. We all know. It is honestly fine.
Happy birthday. I would roast you properly, but Mom reads these now.
You are the reason I have trust issues and also the reason I turned out all right. Happy birthday.
Happy birthday. I have known you your entire life and I still have several questions.
Wishing you a birthday as dramatic as you are. Please set the bar high.
Happy birthday. Legally you are an adult. Emotionally, we have agreed not to discuss it.
Another year, another candle, another photo you will make me delete. Happy birthday.
Warm and short
Happy birthday. You are my favourite person in the world to be quiet with.
Wishing you a gentle, happy day. You hand everybody else one all year long.
Happy birthday. Whatever this year asks of you, you will not be facing it alone.
You are home to me, wherever either of us happens to be living. Happy birthday.
Happy birthday. Thank you for being steady during the years when I was not.
Wishing you every single thing you have quietly hoped for and never said out loud.
Happy birthday. I love you, plainly, with no joke attached to the end of it.
To my sister: you make the hard years survivable. Have a beautiful day.
Happy birthday. I hope you feel today exactly how loved you actually are.
You have been my one constant since the very beginning. Happy birthday, and thank you.
Wishing you a whole day of being looked after for once. Happy birthday.
Happy birthday. Of all the things I never chose, you are the one I would choose again.
Questions and answers
Does a short wish have to contain the words happy birthday, or can you go straight to the line?
Keep them, and put them at the front. In a stream of messages the phrase works as a label: it tells her in one glance what she is looking at, so the sentence after it is read as a wish rather than as a passing remark that needs answering with a question. Position matters more than presence. At the start it frees everything after it to be entirely yours; at the end it works as a sign-off once you have said the warmer thing. Buried in the middle it does neither. The one place you can drop it altogether is a card, where the occasion is already established by the object in her hands and the greeting has been printed on the front for you.
She writes me long birthday messages and I want to send two lines. Does that look like less effort?
Not if the two lines could only have come from you. Effort reads through specificity rather than word count, and one sentence containing something private outranks four paragraphs of general goodwill every time. If the imbalance still bothers you, match her in a different currency instead of in length: send the short message in the morning and phone that evening, or add the one photograph she has never seen. What genuinely reads as thin is a message that is short and generic and late, with nothing following it. Short, specific and on time is not less effort. It is simply a different shape of the same thing.
Is sending it at midnight a nice touch or a nuisance?
That depends entirely on whether she is awake, and you already know the answer. For a sister who is up late anyway, being first is a large part of the point and the message gets read within a minute. For one with small children, an early shift, or a habit of leaving the phone on loud, midnight is not a gesture, it is an alarm. The reliable default is early morning, before the day fills with everybody else’s messages, which is also when yours has the least competition. Late evening works too, once the noise has died down and there is room for a proper reply. The one slot worth avoiding is the middle of the afternoon, when it lands between two other things and gets a thumbs up.
We are not a family that says love you. Does a birthday make it safe to say it once?
A birthday is the one day a sincere line needs no explanation, so yes, but do it deliberately. Put it on its own, with no joke in front of it and none behind it, because the softening is exactly what makes it read as an accident. Then be aware of what you have started: in families these lines quietly become the standard, and leaving it out next year will say something you never meant. If that is more than you want to commit to, plainer wording carries the same weight and sets no precedent — glad you exist, lucky to have you, thank you for everything. She will hear all three the same way, and so will you.
She is my step-sister, and calling her my sister in writing feels like a stretch. What do you put?
Use whatever you call her in conversation, because a card is not the place to settle the question of what you are to each other. If the word sister comes out naturally when you introduce her to somebody, write it. If it does not, write her name and skip the label entirely, since a wish addressed to a person by name is warmer than one addressed to a category. The same holds for a sister-in-law: the honest and easy version is to say what she actually is to you, such as the one who makes family things bearable. Nobody has ever objected to being described accurately and fondly.