On Instagram, "reach" refers to the number of unique accounts that have seen your post. Each unique viewer is counted only once, regardless of how many times they see the post. You can find more information about reach in Meta’s documentation here.
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​Instagram’s Approach for Business Accounts

When you select a 30-day time window, Instagram will count each unique user only once, no matter how many times that user sees the post within those 30 days. This means the total reach displayed by Instagram won’t be the same as the sum of each day’s reach—each user is counted just once per period.

​Polar Analytics Approach

Polar Analytics calculates reach differently because it does not have access to individual user IDs to track unique viewers. Instead, reach is shown as the sum of each day’s reach over the selected period. This can result in a higher reach count in Polar Analytics compared to Instagram, as it doesn’t account for duplicate views by the same users across multiple days.

Key Takeaway
The differences in reach calculations mean you may notice a higher reach total in Polar Analytics than on Instagram for the same period. This variation stems from Instagram’s unique viewer count method versus Polar’s daily sum approach. To compare reach metrics directly, you can export Instagram reach data by going to Meta Business Manager > Insights > Results.