Kris Jenner won't spend quality one-on-one time with her grandchildren because it would cost her too much time and money.

The 68-year-old momager - who is worth an estimated $500 million - loves spending time with her 13 grandkids but joked she has been deterred from trying to "really get to know" them all because of what it would cost her.

She told MailOnline: "I often say to myself that I really should be the kind of grandmother that takes my grandchild to dinner, like once a month.

"Like really get to know your grandchild and see what's happening in school and all this stuff. And I thought if I did that, that would take half a month, just to go out to dinner with my grandkids.

"And I am like, nope not going to do that. They're not getting that out of me."

Kris revealed she recently took her eldest grandchild, 14-year-old Mason - the son of her daughter Kourtney Kardashian and her former partner Scott Disick - for dinner and promised to buy him a car if he stays away from drugs and alcohol for the next two years, but quickly realised she will end up "going broke" if she repeats the gesture for his siblings and cousins.

She said: "I think I did make a little mistake because I took Mason out to dinner, and I was in a really good mood. I probably had a vodka or something, I don't know I wasn't driving.

"But we met at dinner because he likes to go have sushi and I was like, 'Listen if you don't drink or do drugs until you're sixteen, and you can prove it – you know it involves testing and all sorts of stuff – I will buy you a car for your sixteenth birthday.'

"And he loved that and what I realised that I have to do that 13 times. I'm going broke! 13 times."

But Kris admitted it makes her very "happy" to see her grandchildren most days.

She said: "My little thing at the end of the day when I am getting ready for bed, I say, 'How many of my grandkids did I get to see today?' And that’s really a thing I do every single day. I count.

"And yesterday I was at Kim’s office... and some of my grandchildren came in and they were walking by and I’m like, 'Hold on one, two', trying to count to see how far I get. But it’s like my thing. I love it, makes me very happy."

As well as Mason, Kourtney has Penelope, 11, and Reign, eight, with Scott, and four-month-old Rocky with husband Travis Barker. Kim Kardashian has four children with ex-husband Kanye West, North, 10, Saint, eight, Chicago, six, and four-year-old Psalm, while Kourtney Kardashian is mom to True, five, and 19-month-old Tatum, who she has with ex-partner Tristan Thompson.

Kylie Jenner and Travis Scott have Stormi, six, and Aire, two, while Rob Kardashian has seven-year-old daughter Dream with former partner Blac Chyna.

Kendall Jenner is the only one of Kris' children not to have kids of her own yet.