Carrie Underwood is proving once again she's her own best advert, as she modeled her apparel line CALIA on Saturday.  

The 37-year-old old country music superstar took to her Instagram to share a phenomenal mirror selfie of herself in a sporty bikini, which showcased her gym-honed abs. 

'First day of summer!' the seven-time Grammy winner captioned the sultry snap inside her massive walk-in closet.

Tanned and toned: Carrie Underwood is proving once again she's her own best advert, as she modeled her apparel line CALIA on Saturday

As she slipped into a modest black and white swimsuit, the Before He Cheats hitmaker posed up a storm with one hand on her hip and her gorgeous gams on full display.

  

In addition to showcasing her toned and tanned physique, the mother-of-two styled her signature blonde tresses in natural waves. 

Carrie's post comes after her trainer, Eve Overland, revealed to Us Weekly late last month in the week that she will even workout while doing laundry. 

Beauty: In addition to showcasing her toned and tanned physique, the beauty styled her signature blonde tresses in natural waves

'She is dedicated to living as healthy as possible the for 52 weeks of the year,' Eve said.

'Carrie has been known to do walking lunges around the house and jog in place while doing laundry.'

Eve also shared that the Cry Pretty singer's favorite workout is running.  

Fit: Carrie's post comes after her trainer, Eve Overland, revealed to Us Weekly late last month in the week that she will even workout while doing laundry

Dedicated: 'Carrie has been known to do walking lunges around the house and jog in place while doing laundry,' added the fitness expert