37 Best Ways to Say "Happy Birthday, Unbiological Sister"

Having a sister is like having a built-in companion, but if you don’t have any biological sisters, an “unbiological” sister can be just as special to you.

An unbiological sister is even closer than a best friend. She’s someone you can rely on no matter what you’re facing, who will support you, give advice, and listen to your secrets.^[1]

Close friendships between women not only provide emotional support, guidance, and companionship but can also improve your health! A study of breast cancer patients found better outcomes in women with larger groups of friends, even if those friends lived far away.^[2]

On your soul sister’s birthday, it’s lovely to take the opportunity to celebrate her and remind her how important she is to you.

Below, we have more than 30 “happy birthday, unbiological sister” messages, plus tips to help you create your own personalized options!

Thank you for being my one true friend and sister, and for allowing us to do things together instead of competing. I love you! Happy birthday!^[3]
Here’s to bigger, better, and brighter years ahead. May your every wish come true this year, and may you only experience happiness and love. Happy birthday, soul-sister!^[4]
BFF means Best Friends Forever, but do you know what SBFD means? It’s “Sister but Friend in Disguise.” Happy birthday to my SBFD!^[4]
Warm birthday wishes to a special lady who I’m lucky to consider a sister. You are truly remarkable, and apart from being your soul-sibling, I’m blessed to be your friend too. Happy birthday, girl!^[4]
Cheers to another year around the sun. Happy birthday, sis!^[5]
Happy birthday, soul sister! I’m really proud to be your best friend. I look up to you in everything, and I know you will continue to inspire me. Enjoy your day!^[6]
Friends come and go, but family is forever. We might not be family by blood, but I’m honored to call you my sister! Happy birthday!
I’m so blessed to have an unbiological sister like you. You are the greatest and deserve all the happiness in the world on your special day. Happy birthday!^[4]
I don’t know what I’d do without you in my life. Happy birthday, soul sister!^[5]
Happy birthday to you today, my sweet friend! You’re like the sister I never had and you mean more to me than you’ll ever know. I’m confident that we’ll be friends for life and sisters for eternity. Enjoy your special day — you deserve it!^[7]
Happy birthday to my sister at the soul and a friend close to my heart! I hope your special day this year is everything you want it to be!^[7]
We may not be sisters by birth, but we’re sisters at heart and siblings by choice. I couldn’t be luckier than to have you in my life, and I wish you the very best in the coming year! Happy birthday!
On this special day, let me wish you good luck, lots of happiness, and love. In a word, I wish you an amazing life. Happy birthday!^[4]
Happy birthday to that one friend of mine who will always be more like a sister to me! Love you lots, girl!^[7]
Through thick or thin, I can always count on you. That’s why I hope you enjoy your special day to the fullest! Happy birthday, [nickname]!^[5]
My dear soul sister and kindred spirit, I’m sending my best wishes your way on your very special day today. We share a bond unlike any other, and I will always be grateful for having someone as spectacular as you in my life. Happy birthday!^[7]
Sister (noun): a person who knows you inside and out. That sounds like you! I’m so grateful to have you in my life. Happy birthday!^[4]
We may not be sisters by birth, but somewhere deep within me, I feel I’ve known you forever. You’re my true sister, FOREVER. Happy birthday!^[8]
A sister may fight with you, taunt you, scowl at you, or trouble you. But at the end of the day, she’ll always love you. Happy birthday, my soul sister!^[4]
You are the sister I got to choose. I’m so thankful for your friendship. You deserve the very best, and I hope [age] is fantastic for you! Happy birthday!
Happy birthday to one soul sister from another! You mean the world to me, and I hope your special day is nothing short of perfection!^[7]
We weren’t sisters by birth, but we knew from the start… fate brought us together to be sisters by heart. Sister, I love you so much and hope you have an incredible [age] year! Happy birthday!^[9]
In my heart, you will always be a true sister to me first and foremost, and then a friend second. Our bond has grown so strong that, to me, you are like family. May you have a wonderful birthday today!^[7]
If we can’t be biological sisters, at least we can be unbiological sisters for life! Here’s to another incredible year! Happy birthday!^[3]
Some friends are exactly that, and some friends are more like family. You’re the latter. You’re more of a sister than a friend. Happy birthday!^[7]
Sending beautiful birthday wishes to my best friend, who is like family to me. You may not be my sister by blood, but you truly are by heart!^[7]
A special friend I truly adore, in my heart you’ve earned sister status and so much more! Happy birthday!^[7]
Because of you, I laugh a little harder, cry a little less, and smile a lot more. I hope this year you laugh a little harder, cry a little less, and smile a lot more. Happy birthday, sis!^[9]
What do you wish for a sister-like friend as incredible as you, who is already so amazing and who has accomplished so much? Eternal joy and happiness, I guess! I hope that you always find contentment in everything you do and that the good always far outweighs the bad in life. You deserve every happiness! Have a marvelous birthday!^[7]
It’s hard to give up on my dreams when my unbiological sister is my cheerleader. Thanks for all you do, girl! Happy birthday!^[3]
Sending lots of love and wishing you a sweet birthday today, my closest friend and true sister at heart!^[7]
You’re my closest friend and a true soul sister indeed! You’re the driving force behind the amazing things that I do in life. Happy birthday!^[6]
I’ve always longed to have someone I can call my sister. That’s why I’m so grateful for having you around. Happy birthday!^[6]
To the only one who can read my thoughts and moods without glasses, happy birthday!^[3]
Happy birthday to my soul sister! Even though we’re not related by blood, you have loved me more than my own family. Thank you so much. Cheers on your birthday!^[6]
Happy birthday to the best gossip buddy on the planet, my one and only unbiological sister!^[3]
My dear sister from another mister, you are a one-in-a-million find and a priceless diamond. Happy birthday!^[3]

How to Craft the Perfect Happy Birthday Message for Your Unbiological Sister

Your unbiological sister is undoubtedly one of the most important people in your life.

Since she means so much to you, a personalized message might be more fitting than a pre-written one for her birthday.

Keep the following tips in mind to help you write:

Make it personal. Make references to memories, favorites that you share, or dreams she has for the upcoming year. The more personal your message is, the more meaningful it will be for her to read!
Keep it light. A birthday is a celebratory occasion! You and your unbiological sister have probably been through a lot together, but it’s best not to bring down the mood on her special day, so keep your message positive and sweet.
Don’t be afraid to get mushy! While it’s good to keep the mood light, that doesn’t mean you should entirely avoid emotion. If there’s ever a time to share excessively sentimental thoughts and words, it’s a special occasion like a birthday! Use your message to emphasize how much she means to you.