The calculation for line 88 in Schedule J is simple, it is just line 87 times 39%. The calculation seems to work up to values of $45,000 for line 87. For values beyond this number, irrespective of the line 87 value, line 88 will be set at $17,550. Since the Revenue Quebec form does not mention a maximum value for lines 87 or 88, nor for line 24 from which line 87 derives, I assume this behaviour is an error.
Here is a screenshot example:
$55,683.80 * 39% = $21,716.68, but the screenshot shows $17,550.
Please fix. Thank you!
Troubleshooting
My error. Though Schedule J does not explicitly list limits for the values of line 87, there are in fact some. Here is what Revenu Quebec sets them at (note that the line 75 mentionned in the table below is an intermediate step to line 87).
I should have looked before asking the question... Mea culpa!
