New data shows existing tenants are paying less rent than new tenants.
The ESRI has found on average new tenants were paying €214 more per month compared to sitting tenants.
The study, which looked at tenancies registered between April and September 2022, found new tenants were paying an average of €1,517 per month, 16.4% more than the average of €1,303 for existing tenants.
The study, which was funded by the Residential Tenancies Board (RTB), found the biggest differences paid by new and existing tenants was found in the north-west, west and parts of the midlands, with smaller gaps in the east of the country.
The report's author, Dr. Rachel Slaymaker, says the difference between new and existing tenants is up to 25% in some locations.
"Particularly in parts of the North, the Northwest and the Midlands, we generally are seeing new tenants there paying typically between 20 and 25% higher than their existing tenants.
"But actually some of the biggest differences we see would be in Limerick City, in Carlow."
In Dublin, new tenants are twice as likely to be paying more than €2,000 in rent per month. More than one in five existing tenancies are above €2,000, compared to nearly two-fifths of new tenancies.
The report found around a quarter of new tenancies in Dublin are at €1,500 or less per month, compared to two in five existing ones.