In a 5,000-word essay posted in Bullish Cross Monday, Andy Zaky laid out his method for estimating Apple’s (AAPL) quarterly revenue and earnings numbers. He starts with three assumptions:

• That most Wall Street analysts and financial writers are completely clueless and couldn’t analyze their way out of a paper bag
• That the earnings guidance numbers Apple issues each quarter are totally random — red herrings designed to confuse the ignorant
• That almost everything you need to know to estimate Apple’s earnings per share with uncanny accuracy is telegraphed in five guidance numbers: Revenue, gross margin, operating expenditures, other income and expenses (OI&E) and taxes

That’s because, according to Zaky, Apple’s guidance always undershoots its actual results by fixed, predictable amounts. He spells them out:

Revenue: Apple beats its guidance by 12% to 18%
Gross margin: Apple sandbags GM% by 250 basis points, plus or minus 30
OpEx: Add $50 million to get actual expenditures
OI&E: Add $15 million
Tax rate: This one Apple tends to report accurately

Given that Apple’s revenue and gross margin guidance last quarter was higher than it’s ever been, Zaky deduces that the company is expecting record sales of its most profitable two products: iPhones and iPads. Estimating unit sales, says Zaky, requires analysis too complicated to fit into even a 5,000-word article. Suffice it say that he is predicting, with some confidence, that for the first fiscal quarter of 2012, Apple will report:

Revenue: $42 billion
EPS: $11.75
iPhone unit sales: 32 million
iPods: 18 million
Macs: 4.9 million
iPads: 13.5 million
GM%: 42.5

You can read Zaky’s full article here.