Jessica Simpson reportedly "spends half the day" in the gym.
The Weight Watchers spokesperson, who has lost more than 60 lbs. since giving birth to her second child, Ace, last June, has worked extremely hard for her toned figure and runs six miles almost every day.
An insider told Life & Style magazine: "Jessica has gotten her best body ever. She truly feels like she's in better shape than she was in her early 20s.
"She set out to get the best body of her life - and she's accomplished it."
The 33-year-old blonde beauty, who is gearing up to marry fiancé Eric Johnson in Santa Barbara, California in July, with whom she also has two-year-old daughter Maxwell, works out "three to five times a week" with her personal trainer, Harley Pasternak, and spends a lot of her free time on the treadmill.
The source said: "She'll watch TV on it, talk on the phone. Jess probably spends half the day there... She's incredibly proud of the way she's stayed on track."
Jessica recently insisted she had no regrets about gaining weight, as she learnt a lot from the experience.
She said: "I fluctuate, I'm a woman. I feel like we all need to enjoy life. If I'm five pounds heavier or 50 pounds heavier or five pounds lighter, I don't think that should define who you are."

Bruce Willis and Demi Moore's daughter walked around New York City completely topless on Tuesday (27.05.14).
The former couple's second eldest child, Scout Willis, posted several photographs of herself wearing just a skirt and sandals on the streets of Manhattan on Twitter to protest Instagram's nudity policy after her account was suspended.
She captioned one shot: "Legal in NYC but not on Instagram," and another: "What @Instagram won't let you see #FreeTheNipple"
She told her followers that she was boycotting the photo-sharing site after it removed one of her photos - of a sweatshirt she designed, The Babe Bomber, featuring two topless women - for violating its Community Guidelines.
The 22-year-old aspiring singer also tweeted: "If you don't like what you see, simply unfollow me.
"My comfort with my body should not be dictated by how others perceive me. However, I don't wish to force this view on anyone."
She also pleaded to Instagram: "Can I please just have all my photos back??? I won't even have an account anymore I just want my photos!"
'Diehard' star Bruce, who also has daughters, Rumer, 25, and Tallulah, 20, with Demi, as well as Mabel, two, and three-week old Evelyn with wife Emma Heming-Willis, is unlikely to be happy about Scout's protest.
A source previously revealed he was "mortified" after he saw pictures of Rumer showing a lot of skin at a red carpet event.
The insider said: "Bruce was mortified. As every knows, he's actually a very conservative guy and doesn't like to see his daughter parading around in next to nothing."

Lana Del Rey performed at Kim Kardashian and Kanye West's pre-wedding bash for free.
The 'Summertime Sadness' hitmaker hit back at rumours she was paid up to $2.8 million to perform three tracks at the couple's lavish party at the Palace of Versailles near Paris last Friday (23.05.14) on the eve of their wedding in Florence, Italy.
The 27-year-old singer told gossip website TMZ.com: "I would never let a friend pay me to sing at a wedding, that would be crazy."
Asked how much she would charge to sing at a normal wedding, she said: "I'll do it for free like I did this one!"
The couple asked the star to entertain their guests after Kanye, 36, hired an orchestra to perform her hit 'Young and Beautiful' when he proposed to the 'Keeping Up with the Kardashians' star at AT&T Park in San Francisco on her 33rd birthday last October.
Sources previously claimed that Lana had "politely declined" his request to sing the track, which is one of Kim's favourites.
An insider said at the time: "(Kanye) asked Lana to perform for Kim at surprise marriage proposal in San Francisco.
"Lana politely declined, and didn't give any reason for not being able to perform. It was a very firm no from Lana and her camp. Kanye did try to push it, but didn't get anywhere. Kanye decided to hire an orchestra to perform the song for Kim, and he was much happier with how it turned out.
"Kim was bummed that Lana didn't perform for the big event, but she is still a huge fan. She just loved that Kanye tried to make it happen. Kim is jokingly saying Lana will want to perform at their wedding."
The couple also hired Andrea Bocelli to sing at their wedding ceremony and John Legend performed at their reception on Saturday (24.05.14).

Paul Walker's daughter will continue to live with her mother and a nanny.
The late star's mother, Cheryl Walker, dropped her petition to become the legal guardian of his 15-year-old child, Meadow, last month, after reaching an agreement with the teen's mother, Rebecca Soteros, and Los Angeles Superior Court Commissioner David J. Cowan accepted their arrangement and dismissed the case on Wednesday (28.05.14).
Amy Nieman, Meadow's court-appointed attorney, argued that there are "a lot of layers of support for Meadow" to make sure she receives proper care and court oversight was not needed, according to PEOPLE.com.
She added that Rebecca, who is undergoing treatment for alcoholism and is currently sober, has been spending lots of time with Meadow.
The duo will live in a home purchased by the estate of the 'Fast & Furious' star, who died in a car crash in November, with a nanny, who has cared for the teenager for almost two years.
Meadow began living with her famous father full-time in California three years before his death, after moving there from Hawaii, where her mother - who was arrested in 2003 and 2013 for drink driving - raised her.
The youngster is set to inherit Paul's entire $25 million fortune.
Cheryl petitioned for a guardianship over her granddaughter, but she later asked to dismiss it, citing Meadow Walker's wishes.
Her attorney said that she had accepted the arrangement "in the absence of a better plan."

One Direction star Liam Payne admits his drunken Twitter rants are "not good".
The 20-year-old pop star sometimes can't resist going on the social networking website when he's intoxicated and accepts on occasions his comments cause him regret.
Talking to BBC Radio 1 DJ Scott Mills following 1D's performance at the Big Weekend Glasgow 2014, Liam said: "I have a few drunken rants sometimes on Twitter ... Yeah they are quite deep, sometimes I go in hard, it's not good. Then I wake the next morning and it's like - ahhh, old news."
His bandmate Louis Tomlinson, 22, is also guilty of tweeting whilst drunk, admitting: "I've been told to take many [tweets] down, yeah yeah."
One Direction - which also includes Zayn Malik, 21, Harry Styles, 20, and Niall Horan, 20 - were previously involved in a spat with now defunct boy band The Wanted which went online and the boys accept they enjoy a Twitter row.
Quizzed on what posts they take down, Louis said: "Whenever we've got in to the occasional Twitter row, which - back in the day - we used to love."
Liam chimed in: "They are quite enjoyable, a Twitter row."
The group has a love/hate relationship with social network sites - which helped propel them to global stardom - because it can be difficult to brush off harsh criticism but at the same time they're glad they can connect with fans through the medium.
Liam added: "Sometimes they can be horrible places, with the wrong people on there. You tend to notice the bad things on there, but that's the thing, you have to waiver those out and notice the good things. How can we have a hate relationship with social media when it's made us in to this little monster?"

Selena Gomez is trying to get Justin Bieber "on track".
The 21-year-old singer's grandfather Ricardo claims she is trusted to be a "good influence" on the troubled pop star - who was arrested for driving under the influence last year - and while they are no longer dating, they still hang out.
Ricardo said: "She was telling us that she didn't want to be with him because of what he was doing, that he was getting into drugs and it was something she doesn't like.
"They still go out. We worry, not just because of their relationship - we hate to see him in trouble.
"The agents say it is good for her to be next to him, keep him out of the bad habits. They say she has been a positive influence for him. She's doing all she can to get him on track."
Ricardo also opened up about his granddaughter's two-week stint in rehab in January, which was thought to be for exhaustion, but he feels Selena's issues with Justin contributed to her seeking help.
He told Heat magazine: "There was some pressure because [her career] is a lot of work. Plus, she was worried about Justin.
"We saw in a newspaper that she was doing drugs, so I called her. She said, 'No, you know better than that, Pap.' "

George Michael was taken to hospital after collapsing at his home.
The 'Careless Whisper' hitmaker was treated by paramedics at his north London mansion for four hours on May 22 due to a mystery illness before being helped into an ambulance.
Shocked witnesses told The Sun newspaper that two emergency vehicles responded to a 999 call at about 8am and rushed to help the 50-year-old singer, who lives in Highgate in London.
The star was reportedly taken to hospital at 12pm for emergency treatment but his agent has refused to comment on why he suddenly collapsed and whether or not it was related to drugs.
A spokesman said: "George Michael was in hospital for routine tests but there is nothing further to say."
George almost died of pneumonia in 2011 and has had to deal with a number of health problems over the years, including depression and drug addiction, which has seen him arrested multiple times and he served an eight week prison term in 2010.
Last year, he was also airlifted to hospital after he fell out of a car on the M1 and was treated for "superficial cuts and bruises".
Regarding the recent incident, a London Ambulance Service spokesman said: "We were called just before 8am on May 22. We sent two ambulance crews and staff treated one patient, a man, who was then taken to hospital."
Meanwhile, earlier this year the former Wham! insisted he hadn't touched drugs for more than 18 months after smoking up to 25 joints a day.
He said: "I've completely stopped. I have decided to change my life and I haven't touched it for well over a year and half now."

Louis Tomlinson's dad has slammed his reported drug use and called his antics "childish".
The One Direction singer, who appears in a shocking video smoking what appears to be a joint with band mate Zayn Malik, has been blasted by his father Troy Austin, who fears his supposed drug-taking could spiral and affect his career.
Troy told the Daily Mirror newspaper: "I'm worried for him. I do believe that being that famous will be taking its toll on them. I think everyone is concerned it could lead to other things."
The 45-year-old single dad, who hasn't seen Louis for several years, also claims his son promised him he would never get a tattoo or smoke because he wanted to focus on his career.
Troy said: "He said he would never get a tattoo because it was a scar and he would never smoke because it would damage his vocal cords. He's gone the opposite way and I hope it doesn't get worse. It seems the fame and money have changed him.
"It's very childish. They need a serious talking to. I don't agree with it but I smoked it too when I was younger.
"But you should never brag about it. He's got to think of his fans."
In the controversial video, which was allegedly filmed by Louis, 22, during the band's tour in Peru, he is seen joking with Zayn, 21, in the back of a van.
Louis says: "So here we are, leaving Peru. Joint lit. Happy days!"
As a motorcycle police officer drives past them, he also says: "He's having a look. He's thinking, 'I'm sure I can smell an illegal substance in there'. And he's hit the nail on the head."
Meanwhile, the band, including Harry Styles, Liam Payne and Niall Horan, were reportedly pulled into a crisis meeting at Sunderland's Stadium of Light last night (28.05.14), although they made no mention of the scandal during the gig.
Regarding the leaked video, which was posted online, a spokesman for One Direction said: "The matter is in the hands of our lawyers."

Brad Pitt was "struck in the face" at the Hollywood premiere of 'Maleficent' last night (28.05.14).
The Hollywood hunk walked the blue carpet at the El Capitan theater on Hollywood Boulevard with fiancee Angelina Jolie - who plays the title role in the movie - when notorious prankster Vitalii Sediuk jumped the barrier and rushed at the 'Fight Club' actor.
Sediuk reportedly made contact with Brad, but police quickly stepped in and, after a number of officers wrestled him to the ground, he was arrested.
He was taken to a police station and booked on suspicion of misdemeanour battery in lieu of $20,000 bail.
Brad - who raises six children with Angelina - appeared shocked by the incident, but quickly recovered his composure and was seen laughing with a bodyguard as he waved to fans.
Sediuk is notorious for his encounters with celebrities on the red carpet, and last week attempted to put his head up America Ferrera's skirt at the Cannes premiere of 'How To Train Your Dragon 2'.
In January this year, journalist hugged Bradley Cooper around the waist, putting his face in the 'Hangover' star's crotch at the Screen Actors Guild Awards, and a month later, tried a similar move on Leonardo DiCaprio at the Santa Barbara Film Festival.
He was arrested last year at the Grammy awards for rushing onto the stage just as Adele was about to accept an award from Jennifer Lopez and Pitbull.
And two years ago, Sediuk was involved in an angry encounter with Will Smith at the 'Men In Black 3' premiere after he tried to kiss the star on the lips.
The actor dodged two lunges, which both landed on his cheek, before pushing the prankster away and slapping his face.

Beyonce has been named one of the world's most powerful women.
The 'Drunk in Love' hitmaker - who has two-year-old daughter Blue Ivy with husband Jay Z - placed 17th in Forbes magazine's annual list of the top 100 female "icons, leaders, groundbreakers and ceiling crashers" worldwide.
Other famous faces to appear on the 100-strong list - which was topped for the ninth time by German Chancellor Angela Merkel - included media mogul and philanthropist Oprah Winfrey, who placed three ahead of Beyonce at 14, 'Modern Family' actress Sofia Vergara, who was 32nd, talk show host Ellen DeGeneres and 'Maleficent' star Angelina Jolie, who were 46th and 50th respectively.
Lower down in the list, singer Shakira took 58th place, while fellow chart star Lady Gaga ranked 67th and supermodel Gisele Bundchen was 89th.
The annual Forbes list selected women from eight categories or power bases, billionaires, business, celebrity, finance, media, philanthropy and NGOs, politics and technology and they were then ranked according to money, media presence, spheres of influence and impact.
The final 100 is drawn from an initial list of 250 women.

Katy Perry has invited Prince Harry to go on holiday with her.
The 'Roar' singer - who is believed to have ended her brief romance with DJ Diplo - has reportedly always had a crush on the party-loving British royal so is making the most of her newly-single status by inviting him to hang out with her in Miami.
A source told the Daily Star newspaper: "Katy has always had a thing for Prince Harry. So she decided to be cheeky and invite him to spend Independence Day with her and friends in July.
"The message was sent through a mutual pal, and was very casual. Katy didn't want it to look like she was asking him on a date. But she has always had a thing for Englishmen..."
Harry, who recently split from Cressida Bonas, is said to be "tempted" by the pop princess' offer.
Katy is currently in London as part of the UK leg of her 'Prismatic' world tour, following rumours she had parted ways with Diplo last week.
The pair were first linked at the Coachella Valley Music and Arts festival, but things ground to a halt earlier this month because Katy wasn't ready to get back into a serious relationship.
The 29-year-old star was previously married to Russell Brand and split from her last serious boyfriend John Mayer earlier this year after 18 months of dating.

Harry Styles is furious about Zayn Malik and Louis Tomlinson's "stupid and reckless" behaviour.
The One Direction hunk's bandmates were captured on film joking about smoking marijuana as they passed around a suspicious-looking roll-up cigarette as they were reportedly being taken to Peru's Estadio Nacional in Lima on April 27, and Harry is said to be unimpressed by their antics, which were reportedly filmed on Louis' phone.
A source told The Sun newspaper: "Harry is annoyed about the whole debacle. This should be one of the biggest weeks of the band's career with the launch of their UK stadium tour.
"Instead it has been taken over by this controversy. Harry thinks it was a stupid and reckless thing for Louis to allow to be filmed in the first place."
The footage emerged yesterday (28.05.14) while the group are in the midst of the UK leg of their 'Where We Are Tour' and the remaining members of One Direction - Harry, Niall Horan and Liam Payne - were not present in the short clip.
Harry has distanced himself from their behaviour and has even been travelling separately to his bandmates since he isn't "into these antics".
The insider added: "Despite Harry's reputation, he's incredibly professional and mature, and not into these sorts of antics."
Meanwhile, Louis seems worried and is anticipating the "reaction" from fans.
The source said: "He was up checking his phone to see the reaction.
"He understands the whole world is talking and he is trying to work out how to limit the damage."
The boys are set to take on North America from August 1 and there are now concerns about whether the authorities will allow them into the country because of the alleged drug use.
The insider added: "Everything is about America. It would be a disaster if Zayn and Louis had problems. The authorities could make an example of them."