Apple updates their computers every nine to fifteen months or so. If you buy at the beginning of the “product cycle,” you usually get really good bang for their buck: fast components for reasonably prices. Toward the end of the product cycle, deals aren’t as good.

People often ask for advice about whether they should buy that MacBook or iMac; this is especially common on the Ars Technica Mac Board, and I’ve realized that there’s a relatively simply algorithm to determine whether you should buy now or wait. One person, “masonk,” made this handy flow chart, which is explained in words below:

The standard advice:

If you don’t have a working, usable computer and need one, buy it.

Check the Mac Rumor’s Buyers Guide. Has the computer been updated within the last six months? If so, buy it: an upgrade in the near future is unlikely.

If not, are we within six weeks of the World Wide Developer Conference, MacWorld (or whatever January event might replace it), or a “special media event?” Can you wait the six weeks—that is, do you have a computer that’s still usable? If so, wait, as there’s a good chance of product updates.

If we’re not within six weeks of a major event, buy it anyway, as you don’t know when an update might appear.