How many episodes does Naruto: Shippuden have?

How to get close to this number

Multiply the run by the weekly rate again. Ten years of weekly broadcast at around fifty episodes a year gives you five hundred almost exactly, and that is the answer. The longer a series ran, the more reliable this method becomes, because holiday breaks and recap episodes average out across a decade.

The combined total in the explanation is the number people actually mean when they ask how long this franchise is. Splitting a continuous story into two named series is a marketing and scheduling decision rather than a narrative one, so the honest answer to "how long is this" is the sum rather than either part.

A decade of weekly production at this scale is only possible with substantial original material, which is the structural consequence worth naming. A manga chapter does not contain enough for a weekly episode indefinitely, so long-running adaptations inevitably stall. The length is a symptom of the format rather than of the story having that much in it.