Results of the survey done by YouGov on behalf of CAS found that 9% of people always run out of money before they are paid wages, pension payments or benefits.
A further 11% run out of money most of the time.
The charity warned it is a sign of the growing cost-of-living crisis “gripping the country” and reflects a five percentage point increase since last year.
Many people feel they have no option but to take on debt, putting increasing numbers of people at risk of poverty, CAS says.
This is leading to a rise in demand for money and debt advice.
Myles Fitt, financial health spokesperson at CAS, said people are facing impossible choices on spending.
He said: “One in five people running out of money before payday is extremely concerning, given that these figures have seen an increase since 2021.
“A real issue here is that incomes simply aren’t keeping up with costs. Social security payments like Universal Credit effectively fell in real terms this year, and that was after the decision last autumn to remove the £20 per week uplift to the benefit.
“If people are worried or struggling with money we would encourage them to seek advice from the Citizens Advice network. That can mean our online self-help tools like moneymap.scot or our public advice site, or from a local CAB.”
The charity is calling for more to be done to help people in the coming months and is urging policymakers to “take every measure they can”.
Mr Fitt added: “Advice plays a key role and the difference it makes can be truly life-changing. One in five people saw a financial gain after getting advice from a CAB last year, and the value of those gains were a staggering £4,400.
“We’re here to help, our advice is free, confidential and impartial and people shouldn’t hesitate in coming to us.”
A UK Government spokesman said: “We recognise the pressures on the cost of living and we are doing what we can to help, including spending £22 billion across the next financial year to support people in Scotland and across the UK.
“For the hardest hit, we’re putting an average of £1,000 more per year into the pockets of working families on Universal Credit, have boosted the minimum wage by more than £1,000 a year for full-time workers and our Household Support Fund is there to help with the cost of everyday essentials.”