UPDATE 1-Dollar Tree's quarterly comparable sales miss estimates

(Adds details, shares)

May 25 (Reuters) - Dollar Tree Inc, the biggest U.S. dollar-store chain operator, reported lower-than-expected quarterly comparable sales on Thursday, sending its shares down about 3 percent in premarket trading.

Overall sales at stores open for more than a year rose 0.5 percent, below the 0.9 percent increase expected by analysts polled by research firm Consensus Metrix.

Sales at comparable Family Dollar stores fell 1.2 percent, compared with the 0.1 percent rise expected by analysts.

The Family Dollar chain caters mainly to lower-income customers and was bought by Dollar Tree in 2015.

Several retailers have highlighted the impact of delayed tax refunds on their first-quarter sales.

Income tax refunds started later this year for low-income earners due to a new law requiring the Internal Revenue Service to wait until Feb. 15 to issue refunds related to some kinds of tax credits.

The company's net income fell to $200.5 million, or 85 cents per share, in the first quarter ended April 29, from $232.7 million, or 98 cents per share, a year earlier.

Dollar Tree said it recorded an impairment charge of $50.9 million due to non-payment by Dollar Express for stores bought from the company.

Dollar Express is in the process of liquidating and is in default of its obligations and not cooperating, Dollar Tree said.

The prior-year quarter had also included a one-time tax rate benefit of 9 cents per share, the company said.

Excluding items, the company earned 98 cents per share, in line with the average analysts' estimate, according to Thomson Reuters I/B/E/S.

Net sales rose 4 percent to $5.29 billion, also matching the average analysts' estimate.

The company's shares were trading at $75.90 in premarket trading. (Reporting by Sruthi Ramakrishnan in Bengaluru; Editing by Sriraj Kalluvila)