Check caption length against platform limits.
Two limits apply to a social caption and only one of them is the published maximum. Instagram allows 2200 characters but shows roughly 125 before collapsing behind a More link; TikTok shows about 100. That truncation point is the real constraint, because it decides whether anyone reads past the first line. Hashtags count against the character limit too, and at around thirteen characters each including the separator, eight hashtags consume over a hundred characters — enough to matter on X where the limit is 280. The practical rule is to front-load meaning before the cutoff and place hashtags last.
Total length
Characters = caption length + hashtags x (average hashtag length + 1 separator)
Headroom
Remaining = platform limit - total characters
Because most readers never tap More. On Instagram roughly the first 125 characters are visible in feed, so that is your entire opportunity to earn the expansion. A caption whose point arrives at character 400 is functionally invisible to the majority of the audience.
Either works for reach, but putting them in the first comment keeps the visible caption clean and preserves the character budget for the hook. If they are in the caption, place them after a few line breaks so they fall below the truncation point.