It was confirmed yesterday that a first cut of 0.25% would be announced shortly, with further cuts set to follow.
The bank has been criticised in recent months for its 5.19% variable rate, the biggest in the country and more than 2% higher than the rate charged by AIB.
That has meant that Permanent TSB customers have been paying around €300 a month more on a €300,000 mortgage than a customer on a same-sized loan with AIB.
The first rate cut of 0.25% is expected to save around 80,000 customers €15 a month for every €100,000 borrowed. It is expected to save the average customer around €540 a year.