It just takes doing a little math. If you’re nervous, you can draw it out.

Let’s say your pattern calls for an increase on the first and every 6th row for a total of 10 increases. If x’s are increases and -'s are rows without increases, it looks like

x-----x-----x-----x-----x-----x-----x-----x-----x-----x

and you can see there’s 55 rows involved. At the required gauge of 4.25 rows to the inch, the shaping is taking place over (55 divided by 4.25) 13 inches. Thirteen inches of rows at 5.25 to the inch is going to be (13 times 5.25) 68.25 rows. So you need to somehow squeeze in 13 extra rows.

If you’re a perfectionist, you also need to find a way to accept that you can’t knit a row that’s one quarter the normal height, and so your sleeve will be one eighth of an inch shorter than the pattern. .

Inserting one extra row between each decrease gets us to 64 rows.

x------x------x------x------x------x------x------x------x------x

Look at the picture of the finished item and decide where the last four rows should be slipped in. If it’s just the average run o’ the mill sleeve, the increase can be more gradual at the start, so we can put one extra row between the first 5 increases:

x-------x-------x-------x-------x------x------x------x------x------x

So it would be increase, then increase every 8th row 4 times, then every 7th row 5 times.

Note: I’m writing this at 2:14 am in a fit of insomnia. The theory is correct even if my drawings or actual math is off