By Tatyana Shumsky 

NEW YORK--Gold prices rallied Friday after a weaker-than-expected reading of U.S. economic health fanned investor interest in the haven asset.

Gold for April delivery, the most actively traded contract, rose $23.30, or 1.9%, to settle at $1,279.20 a troy ounce on the Comex division of the New York Mercantile Exchange. Gold futures ended January up 8%, the largest monthly gain since January 2012.

The U.S. economy expanded 2.6% during the final quarter of 2014, the Commerce Department said Friday. This was a slowdown from 5% growth clocked during the third quarter of last year, and it lagged the 3.2% growth rate economists had expected.

Gold prices extended early-morning gains on the news as some traders bet that the Federal Reserve would hold off on raising interest rates amid signs that growth remains uneven. The U.S. central bank has previously said that any shifts in monetary policy would hinge on a steady economic recovery. On Wednesday, Fed officials said they would be patient in raising interest rates, a move expected in the second half of 2015.

"Signs are now pointing to the Fed needing to exercise that patience, so we are seeing a relief rally in the metals," said George Gero, a senior vice president with RBC Capital Markets Global Futures.

A move to tighten monetary policy is expected to push gold prices lower. Gold doesn't pay interest or dividends and could struggle to lure investors away from Treasury bonds and other interest-bearing assets when rates are climbing.

Still, gold prices are likely to benefit from a revival of concerns about Greece. The eurozone member's new leftist leadership has started to deliver on bold anti-austerity campaign promises after a sweeping victory in Sunday's elections.

Recent investor polls point to a 24.3% chance the euro will break up in the next 12 months, as a result of Greece leaving the currency union, said Julian Jessop, head of commodities research at Capital Economics, in a note. This is up from a low of 7.6% in July last year.

Mr. Jessop said that as concerns about the euro escalate, gold prices will also march higher. He expects gold prices to recover to $1,400 an ounce by the end of 2015.

Settlements (ranges include open-outcry and electronic trading):

London PM Gold Fix: $1,260.25; previous PM $1,268.75 
Apr gold $1,279.20, up $23.30; Range $1,257.50-$279.50 
Mar silver $17.208, up 43.5 cents; Range $16.815-$17.320 
Apr platinum $1,238.20, up $20.90; Range $1,217.70-$1,242.50 
Mar palladium $772.40, up 80 cents; Range $770.25-$784.00 

Write to Tatyana Shumsky at tatyana.shumsky@wsj.com