It’s your sister’s birthday, but you live far away and can’t be there to wish her Happy Birthday in person. Don’t worry – we have you covered! Get inspired by our editor-approved letter samples, then personalize and send your own letter or pick one from the below collections and send to her.
Happy 18th Birthday Sister Letter
- Happy 18th Birthday! I hope it’s the best one yet! As your older sister, I must guide you through life. I hope my love for you shines through as I write this, for it is genuine and pure. You are a special person and I couldn’t be more proud to have you as my little sister.
- I love you! You are my precious sister and words can’t express the joy your presence brings me. I hope that I made your day as wonderful as you have made mine, but I know we will continue to keep one another smiling and laughing. You were such a blessing to me when you were born, but now I am blessed every day by your sweet laughter, a warm hug, and kind heart. Happy 18th birthday!
- I love you so much. I don’t have a single doubt in my mind that you are the most wonderful sister anyone could ever dream of having. I am so glad we found each other and I cannot wait to see all the amazing things that life has in store for you! HAPPY BIRTHDAY, SISTER!
- There’s no one quite like you, you are wild and free. You always have been and always will be. I love you, baby sister! Today we celebrate your 18th birthday and many more to come.
- Happy 18th birthday! Although I know you are reading this, I wanted to write and let you know how much you mean to me. You are a beautiful person inside and out, and your 18th year should be filled with joy, laughter, and love.
- Dear sister, even though you have grown up so much, there is still one thing that will always remain the same. That is my love for you, my darling sister. I love you to the moon and back!
- If there is one thing that I would wish for you, it would be happiness. You’ve had some hard times these past few years, but I can tell that there is a brighter future ahead. As you grow older and make your own decisions, remember to stay happy. I love you!
- I know there aren’t many that can say this but I am so happy about your birthday. I hope you had the best day, and most of all I hope that you find what you’re looking for. You deserve the best and when you are older I know you will be able to find it.
- I always said that I would be the one to finally find my soul mate, and I believe that you are my soul mate. I am so lucky to have someone like you in my life. In this crazy fast-paced world sometimes it’s hard to find time for yourself, but for you, I will always make time. Thank you for being in my life.
- Happy 18th birthday to my little sister! I remember being 5 and playing with you in mom’s closet. I could never stop laughing at the things you would wear as clothes. You were always so silly! Now as a young adult, I still think of you every day. You are my little sister and such a beautiful woman. I am beyond blessed to have you in my life!
- Happy birthday to my best friend, the only sister I would ever want. I wish I could be there to celebrate with you and your family. Missing you today, but memories of the past keep me smiling.
- I remember the first day I saw you and reminded me a lot of myself. We were so young, but I still knew how much you meant to me already. I was happy that we became such good friends and I knew there would be many more happy days ahead of us. I love you so much and I won’t ever forget that special little girl who made my world an even better place. Happy birthday!
- Even though were not dating, I still want you to know how much I miss you, how much I love you, and that your birthday is the best day ever! I got your work schedule for the next two weeks and am planning a day out for us. You better call me. I adore you beyond words, if only we were dating still.
- You are my very best friend and I couldn’t imagine life without you. I love you more than words can say and I have so much fun with you. You mean everything to me!
- You are my sister, my best friend and more, in one package. I love all the fun times when we were growing up…all the late-night talks, adventures, and fights. I am so glad that our paths crossed.
- You were there with me every step of the way on my serious journey to adulthood and I am filled with so much love for you.
- I’m so glad to call you my sister. I’ve always looked up to you, and now more than ever I consider you my role model. I will be praying for you tonight as you celebrate your 18th birthday. I’ll never forget the time we spent together growing up, or watching over our little brother and sister. Happy birthday, big sis!
- Oh, my glorious sister, I cannot begin to put into words how much I love you. You have been my best friend since day one, and I can’t wait to see what the future holds for us. To me everything about you is perfect. Your eyes, your smile, your hair, even your nose (I might be a bit biased here). The love I have for you grows stronger by the second! Happy birthday!
- To my loving sister: I want you to know how much I love and appreciate you. You have taught me so many things in life, and I’m glad that we will be spending the rest of our lives growing up together. Love always, your favorite little sister
- You deserve the best life has to offer, and because of that, I hope you enjoy your special day. My dearest sister, I want you to know how amazing you are and how proud I am to call you my sister. I’ve always been there for you from the first day. You and I have shared so many great memories, more than most sisters can even say they have. I’m glad that we get to celebrate today! I love you so much!
- You are my best and only sister, and I just wanted to tell you that I love you and I hope that you have a great day. Hugs and kisses from your sister!
- I woke up this morning and the first thing I thought of was you. As I lay in bed counting the minutes before I could call you, all I could think of was how lucky I am to have such a beautiful sister in my life.
- Happy Birthday! You are so full of life and I’m glad to have been a part of it. I hope you know that if you need anything, don’t hesitate to call! I want to spend this day celebrating with you.
- Dear baby sister! I’m so glad to have you as my little sister and more than anything that you are 18 years old. I can’t believe I’m already an aunt! So, as a present for your birthday, I want you to know that no matter what happens in life, you will always have a family who loves and cares about you. We love you so much! Be happy because we all love you!
- Writing this letter to you with my heart full of emotions makes me reflect on how much you’ve grown. I know that 18 is just a number, but it has special meaning for you now. It means independence, a license, and more responsibilities. I’m so proud of all your accomplishments and I look forward to seeing what the future brings my baby sister!
- Sister, I know how hard it is to be eighteen, but you will get through it. You were always there for me, so now it’s my turn to be there for you. You are the greatest sister in the whole world and I just want to say that I love you with all my heart!
- There is so much I want to say, but words cannot express how happy I am that you are now 18. We have shared so much in the last 18 years and I wouldn’t change a thing. You have taught me so much about life, the importance of friendship, and the meaning of family.
- Happy birthday, big sister. I feel like I can always come to you when in need of some advice or even just someone to talk to. You’re always there for me and everyone else. You help me out a lot and I just want to say thank you for being you!
- There just aren’t any words to express what your life means to me. You are my best friend, my partner in crime, and the sister I never had. I will forever cherish the memories we have of growing up together and I look forward to making many, many more memories with you in the future! Happy Birthday! I love you!
- You are my best friend and sister. I am so happy to have gotten to be a part of your life, growing up and watching you live your biggest dreams! I look forward to many more years of laughter, cheers, and memories! Here’s to a
- Hey sweetie! I was thinking about you earlier & thought I’d touch base. I just wanted to tell you how much I miss you and how excited I am that we are finally going to be together again this summer! You are my best friend in the whole world & I love you more than anything else in this world…
- You are and always have been an amazing sister. I love you so much! I couldn’t be happier to have you as part of my life. I’m proud to call you my sister, and even more proud to share a birthday with you. I hope that your day is amazing and that the years ahead of us are happy ones.
- The day you were born, my life changed and I truly believe that my future started. I’ve always been there for you, not just as a sister but as a friend to share secrets with. Now you’re moving on and I want you to know how much I love and support you. Great big hugs and happy birthday.
- Dear sister, you deserved this card so much more. You’re so amazing. I couldn’t have asked for a better big sister. I would miss you dearly if I didn’t have a sister as awesome as you are. I love you with all my heart and will always be there for you!
- An amazing night, wonderful food. Can’t have a party without a cake. I love you more than you could know. You will always be my sister and I will always be your best friend. It’s hard for me to imagine life without you in it. It only falls more perfect because of it.
- Today is your day! Today is a very special day for you – the day you were born. I hope it will be special for me, too. I am glad to have a sister like you. I love you and I wish you all the best in life (both of them).
- We’ve got a weird relationship, but I’ve never loved you more than I do today. No one can take your place in my heart. It’s been a great ride and the story doesn’t end here because it just keeps getting better and better. Love you lots!
- Remember when I used to drive you crazy when we shared a room? I love that we get to share our everyday life now. Sometimes, when you’re working late, I make dinner and bring it to you so that we can share our meal. That’s how much we mean to each other now.
- Happy 18th Birthday!!! I know the opening of this card is starting to get boring, but believe me, it’s from the heart. You’re on the brink of adulthood and all its responsibilities. I can’t imagine you as an adult because that means I’ll have to admit that I am getting old. You are growing up so fast and soon you’ll be driving cars and drinking alcohol, and you won’t need your big sister
- You have always been there for me even when I didn’t deserve it. You are the best sister I could ask for and no matter what I will always be here for you. As you get older and start a life of your own, know that I am here to support you no matter what comes your way. You are mine and I will always love you!
- You are my best friend in the world, and the sister I never had. You give me the joy of having a sister and I am eternally grateful for you. My happiest moments have all been spent with you, and I couldn’t imagine being happier. I love you with all my heart!
- You are the sweetest sister I know. You are the one that brightens my day when I am sad and the one that reduces my stress during large projects. All my life you have been my rock, and everything is better with you around. I love you so much and I treasure our sisterhood!
- Happy 18th birthday to my amazing big sister. You are more than a sister – you are my best friend. I will always be there for you – through thick and thin. I love you, sis!
- I can’t believe you’re 18 today! I am so proud of you, Octavia. You are a shining light to me, your friends, and your family. Each year you have grown into such an admirable young lady and I believe only great things will come of you in the years to come.
- You are my little sister, and I am so proud to have you! Your sweet 18th birthday made me remember how far we have come. I am so glad that we can share the same birthday. I love you so much and can’t wait to see what else the future has in store for us!
- Happy Birthday to my adorable sister! I hope today is an amazing day for you. I just wanted to stop by and tell you how much I love you. You are truly the best sister ever, one of my best friends, and a strong person. Everyone loves you so much and for great reason! Happy birthday, I am so proud of you!
- I want you to know how much I love you. You always bring a smile to my face and you are the best sister. No other sibling could ever replace you in my life, you are too special. I hope that your life is filled with nothing but joy and happiness!
- You are so talented and I am so proud of you! I know that you will accomplish great things. Good luck in college and with your future. I know we will be able to completely reconnect and finish the business of growing up when you move back. I love you, your brother too!
- You are my rock and the reason I get up in the morning. I am so proud of you, of everything you have accomplished, and all your hard work that has paid off. You are one of the most amazing people I know and I am so glad to be able to share a birthday with you. Happy 18th birthday!