Tracy Tyler, 37, said it was only when partner Adam Young offered to foot the bill for calling Camelot after scooping Saturday's jackpot that she got in touch with the Lotto organiser.
Frugal Ms Tyler and her long-term partner, from Epping in Essex, have yet to spend a penny of their new £5,819,806 fortune.
The couple said they had concerns about paying the bills after 30-year-old Mr Young was made redundant from his warehouse job in May. But they are now planning "a few fancy treats", including a new Range Rover to replace Mr Young's battered Citroen Saxo, and arranging his first trip abroad.
"The lottery was an 0845 number and I was a bit worried that would cost me money," Ms Tyler said:
"But he (Mr Young) said he would pay for it so I said all right.
"I don't like to waste money, I'm very cautious."
Ms Tyler said she had learned to live on a budget over the years, living in rented accommodation with Mr Young and their two young children.
"We had managed to make enough phone calls and juggle things around. I was quite good at juggling after years of practice.
"Occasionally I had to ask my mum to help me though.
"Now that stress has gone."
Ms Tyler toasted her win with "a large vodka and coke", and a family trip to the swimming pool the following day.
The couple said they are acutely aware of how their life has changed in the last week, with Mr Young, originally from Boston in Lincolnshire, formerly spending several hours every day looking for work.
Speaking from a hotel in Essex, Mr Young said: "This time last week, we certainly weren't sitting by a pool in the sun.
"I was online looking for jobs. I worked in a warehouse, I had been there for eight years.
"I spent a couple of hours every day applying for jobs, sending my CV off. A few were planning to get back to me this week, so we will see what happens.
"I could yet be offered a job so I would have to make the decision whether or not to take it, or take a sabbatical or something."
The couple said they have yet to check whether their winnings have been paid in to the bank, but plan to spend some money on buying their own home.
They also plan to get advice from Camelot on how to deal with such a huge jackpot.
Ms Tyler, who said she is continuing to play the lottery, added: "If there was one more person in front of me in the queue when I bought my ticket, it could have been completely different.
"We have been very lucky."