According to Diabetes Australia, the recommended amount of weight gain in pregnancy depends on your BMI before becoming pregnant. Generally, you should aim for about 11.5kg to 16kg.
Trainer Don Saladino posted his own message to the actor, saying he "couldn't be more proud" of her staggering loss.
Speaking to Entertainment Tonight in 2015, Mr Saladino said that Lively ate a good mix of foods, and didn't punish herself for cheat meals.
"I think the beauty of the approach she took is the approach I'm trying to get most people to take, is that shorter is sweeter," he explained.
"You don't need to go in 60 to 90 minutes, two hours a day. It's something, where if you only have 20 minutes in the bag that day, go on what you have, get some good work in, try and break a little sweat and get out! It's better than taking off."
Lively's post, which has received more that 1.4 million likes and 8000 comments, with fans congratulating the mum-of-two on her efforts.
"Thanks for being so real!!! You look awesome, that hard work pays off," one comment read.
"Thanks for the realistic reminder," another added. "I beat myself up because I haven't lost all the weight after 8 months."
Lively, who is married to fellow actor Ryan Reynolds, gave birth to her second daughter Ines in September 2016. She also has a three-year-old daughter, James.
Former Biggest Loser trainer Tiff Hall recently shared her weight loss journey, following the birth of her first child Arnold in September.
Hall gained 30kg during her difficult first pregnancy, and admits to being "sick the whole time right up until my last contraction".
In January, the fitness guru revealed she'd lost 21kg โ just four months after giving birth.
"I couldn't do a full squat. I had to use the couch. The fact that I couldn't do a push up โฆ It's so strange. My body collapsed because my core was so weak," Hall said.
"I've had to start on the lowest fitness level. I have a long way to go. My goal is to get up to five push ups on my knees. I've had to really work hard and it's given me a greater appreciation for others who start from scratch with no strength.
"I have so much more empathy now, because I could deliver the exercises before [giving birth] but now I really understand how frustrating it is for new mums.
"I don't regret a single kilo or sausage roll and I know when the time comes to get fit and be back in shape, I'll be able to do it," Hall said.
"I may never get back to my size six hips and my washboard abs, but I'm comfortable with that."
