April 23 (Reuters) - Real estate investment trust Equity Residential, which owns and manages apartments across the U.S., beat first-quarter FFO estimates on Tuesday due to strong rental demand and relatively lower supply in East Coast markets such as New York and Boston.

While rental supply remains elevated across the U.S., the supply pressure relative to demand is less acute on the East Coast as opposed to the Sunbelt region, which includes cities such as Austin and Los Angeles.

About 95% of Equity Residential's net income has been coming from its established markets, where supply levels are more stable, with the company's customers on average spending about 20% of their income on rent.

"The positive demand dynamics in our affluent renter demographic, limited new apartment supply in our existing predominantly coastal markets and our laser focus on expense management continue to produce good results," said CEO Mark Parrell.

The percentage of residents renewing their leases in the first quarter dropped to 4.7%, compared with 6.2% last year, while physical occupancy marginally increased to at 96.3%.

Equity Residential reported funds from operations (FFO) of 93 cents per share in the quarter ended March 31, compared with analysts' estimate of 91 cents per share, according to LSEG data.

The company's quarterly same-store revenue increased about 4% from a year ago. (Reporting by Ananta Agarwal and Nathan Gomes in Bengaluru; Editing by Alan Barona)