Meanwhile, six in 10 people who were helped by the service were forced to take out loans while they waited for the payment, which merges six benefits into a single monthly one.
Gillian Guy, chief executive of Citizens Advice, said: “Half the people we help with a Universal Credit claim are still struggling to keep a roof over their heads while they wait for their first payment.
“Changes to the waiting period for first payment have improved things for many people, but our evidence shows they don’t go far enough.
“Universal Credit must continue to be reformed so it works for all claimants and leaves people with enough money to live on.”
Just under half of those who sought advice from the service had no money left after buying essentials including food, transport and covering housing expenses, the Managing Money on Universal Credit report found.
While the one-week reduction has improved circumstances for some claimants, Citizens Advice is urging the government to make Alternative Payment Arrangements more widely available, which would allow rent to be paid straight to a landlord, as well as more frequent payments.
The report also found that slightly more payments were being made on time since 2017, with 1 in 6 people now not paid in full and on time, compared with 1 in 4 previously.
It comes after the government announced a £39 million in funding for Citizens Advice and Citizens Advice Scotland last October, which from April will provide a Universal Support service to help people manage their claim.
The Department for Work and pensions said in a statement: “Most people on Universal Credit are happy managing their money, but budgeting support is available for anyone who needs extra help. Many people join Universal Credit with existing rent arrears, but this falls by a third after four months.
“We will continue to work closely with Citizen’s Advice and other stakeholders to develop our approach in order to provide the best possible support for all of our claimants.”