Later today Apple will announces its fiscal results for the quarter ending in late September. The fourth quarter of Apple’s 2011 financial year are those to be watched carefully, most notable this year for the back to school Mac sales and how iPhone 4 sales may have tailed off in the face of heavy refresh rumours.

Apple yesterday announced that it had sold over four million iPhone 4Ss in the first weekend of sales and that 20 million customers had signed up for iCloud with 25 million installing iOS 5 on their devices. Of course with these product and service releases occurring after the end of Apple’s fourth quarter we won’t know the full story until early next year.

The results will be announced at 4.30pm ET (9.30pm London) with an Apple webcast being held half an hour later.

Looking at the financials the estimates from the market as taken by Thomson Financial point towards Apple announcing quarterly revenue of $29.45 billion which equates to earnings per share of $7.28. Although the market is always famously inaccurate, Apple 2.0 offers estimates from the most accurate analysts as revenue of $33 billion and EPS $8.88.

Last quarter Mac sales failed to impress Wall Street with analysts at the time expecting sales of 4.2 million but Apple only achieving 3.95 million. This quarter, which encompasses the famous back to school period, the street is expecting Mac sales of 4.5 million.

The big number is of course iPad sales, during Apple’s fourth quarter last year the company sold 4.19 million. Estimates this year place that number at almost 12 million, representing an 185% climb from the year-ago quarter.

The fourth quarter of 2011 was also notably lacking an iPhone product release which it has seen in the previous three years. Questions of whether heavy rumours towards an iPhone refresh will have knocked sales have been playing on the minds of most analysts. During the year-ago quarter, in which the iPhone 4 was released, Apple sold 14.1 million iPhones. Estimates for this year predict a massive climb with some rising as high as 22 million units.

Finally iPod units are expecting to plunge again. Last year Apple announced a 11 percent unit decline in iPod sales at a smidgen over 9 million, this year, despite strong iPod touch sales, Apple is expected to only announce figures of 7 million.