From Michael Rapoport and Theo Francis' The Investment That Cost Apple $9 Billion in 2018, in Friday's Wall Street Journal ($):
Like many large companies, Apple has used much of its windfall from the 2017 tax overhaul to buy back shares. But the recent plunge in stock prices has made that look like a bad idea. Apple and companies including Wells Fargo WFC -0.13% & Co., Citigroup Inc. and Applied Materials Inc. AMAT 2.97% repurchased their own shares at rich prices, only to see their value decline sharply...
Apple, one of the market’s biggest repurchasers, spent about $62.9 billion on buybacks in the first nine months of 2018, according to securities filings. But the selloff has weighed on its shares.
The company’s repurchased shares were worth about $53.8 billion as of Wednesday’s close, some $9.1 billion less than it paid for them. Apple repurchased shares at monthly average prices as high as $222.07, according to securities filings. The stock closed at $157.17 Wednesday...
“Apple makes iPhones. Timing the market is not what they do,” said Howard Silverblatt, senior index analyst at S&P Dow Jones Indices. Companies that try to time the market in buying back shares “are going to be in the red at times.”
My take: What Silverblatt said.
See also: Look who's buying Apple