Every set-in or raglan sleeve tapers from a wider upper arm down to a narrower wrist, and the core taper math is identical between the two: total stitches to remove, divided across the sleeve's length, evenly spaced so decreases don't bunch up. Where the two constructions differ is what happens at the top of the sleeve, where it joins the body.
The shared taper calculation
Upper-arm stitch count minus wrist stitch count gives the total stitches to remove. Dividing that by how many stitches a single decrease row removes (commonly 2, one at each edge) gives the number of decrease rows needed. Those rows then get spread evenly across the sleeve's total row count, which almost never divides perfectly, so most sleeves alternate between two interval lengths (for example, decreasing every 6th row some number of times and every 8th row the rest) rather than trying to force a single interval that doesn't divide cleanly.
Worked example
An upper arm of 72 stitches tapering to a wrist of 40 stitches removes 32 stitches total. At 2 stitches per decrease row, that's 16 decrease rows. If the sleeve is 140 rows long, spreading 16 decrease rows across 140 total rows works out to roughly every 8-9 rows, so a typical schedule alternates "decrease every 8 rows" and "decrease every 9 rows" to land exactly on 16 decreases by the end.
Set-in sleeve caps
A set-in sleeve stops its wrist-to-shoulder taper, then shapes a separate sleeve cap: a curved top edge cut to match the armhole opening on the body. That cap shaping is its own calculation, roughly matching the armhole's depth and width with a mix of a straight bind-off at the underarm followed by a curve of decreases, aiming for a smooth curve rather than sharp angles so the cap seams in without puckering.
Raglan shaping
A raglan skips the separate cap entirely. Instead, the sleeve's upper taper continues in a straight diagonal line all the way to the neckline, with decreases worked at a steady, usually every-other-row interval on both the sleeve and the body's raglan lines simultaneously, so the two pieces (or all four pieces, in a seamless top-down raglan) grow toward the neck at matching rates. Because the raglan line is a constant-rate diagonal rather than a curved cap, its math is simpler to calculate directly by comparing total raglan rows to total stitches removed, without the two-stage cap-then-taper structure a set-in sleeve requires.
Both constructions land at the same underlying goal, an armhole opening the sleeve fits into cleanly. Raglan's constant-rate diagonal makes it easier to modify on the fly (useful for improvised, top-down, or seamless designs), while a set-in cap gives a more tailored shoulder line that a fitted, structured garment often calls for.