The smiley youngster showed off her milk teeth in the later snaps, while an earlier one showed Summer wrapped up in a purple blanket, lying in her cot.
Becky expressed her astonishment at how quickly time has passed as she wrote: "At 7am 8th June last year my beautiful baby girl was born! I can't believe Summer is turning 1 today. She has brought so much happiness, love and laughter to my life. Happy birthday."
Rebecca Adlington's daughter Summer turned one
Over the weekend Becky threw an early birthday party for her daughter at home. She bought a cake which featured an elephant topper and a bright orange number one candle, and decked her house with bunting.
Her adorable birthday girl, who wore Minnie Mouse ears, was also pictured playing in a ball pit.
Becky reunited with her estranged husband Harry Needs for their daughter's bash
Becky, 27, invited her closest friends and family to the bash, including her estranged husband Harry who she separated from in March. The pair dote on their daughter and have made it clear that their priority is to co-parent their little girl.
"Such a lovely day," wrote Becky after the celebrations. "Even though Summer's birthday isn't until Wednesday we had a little party today. She absolutely loved it. Can't believe my little girl is turning 1."
The former Olympic swimmer regularly updates fans with her daughter's milestones. She recently uploaded a video of Summer taking her first steps unaided.
"Can't believe my little girl is turning 1," she wrote
Harry, likewise, often calls his daughter his "bestest friend" and "number one" on Instagram. A couple of weeks ago he shared a picture of himself and Summer playing in the park – a welcome distraction after a particularly difficult week.
"Tough weeks make tougher people right? Looking forward to signalling this one off," he wrote in one snap, followed by: "And then on the flip side of life, my one constant makes every day feel better. So glad I've had this one by my side this week #bestestfriends."
Becky and Harry announced their separation in a joint statement, saying: "We move forward with respect for one another and our focus and commitment is on parenting our gorgeous daughter Summer."