Despite being a gym buff who often posts videos of her workouts, Kim Kardashian West has revealed she's gained 8kg over the past year-and-a-half but is looking to get back in shape in time for her 40th birthday.

The Keeping Up With the Kardashians star, who turns 40 next year, shared on her Instagram stories that she has "fallen off" the intense exercise wagon and her eating habits have led to weight gain - which is in no way apparent in these bikini shots of the mother of four taken over Halloween.

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Harvard Law.... What? Like it’s hard???

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The creator of KKW Beauty and Skims body contouring range says she's opted to try working out before dinner and admits she'll "have to get back into it at some point."

"Sometimes we fall off and need to get it together," she says.

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She goes on to tell her 151 million followers that she just needs to have an ideal goal weight and "work out at all costs".

Working with her personal trainer, Kardashian reveals she has a "major goal" she's hoping to achieve by the time she hits the big 40.

"It's my eating, I work out but it's like, my eating," she says.