How the estimate works
Every platform bills for duplicates somewhere. HubSpot, Klaviyo, and Mailchimp price by contact or profile tiers, so each duplicate is a record you pay for twice. Salesforce charges for data storage past your allowance. Shopify duplicates get your campaigns twice through connected email. The calculator multiplies your duplicate count by the platform's marginal list-price rate — assumptions are shown under the result, and you can change every input.
Why some platforms show no send cost
The wasted-sends tile only carries a dollar figure where a platform actually bills per email. HubSpot includes sending with Marketing Hub and Salesforce doesn't send marketing email at all, so for those the tile reads n/a — their whole duplicate cost already sits in the contact or storage figure, and pricing the sends separately would count the same duplicates twice. Klaviyo and Mailchimp duplicates do receive every campaign twice, so the tile shows how many sends that wastes, but the fee for them is baked into the profile or contact tier. Shopify is the one platform where sends are the bill: Shopify Email charges per message, so the doubled sends are the cost.
Where duplicate rates come from
Teams that have never deduplicated systematically typically find duplicate rates between 10% and 30% when they first measure. If you don't know yours, run an export through the free CSV dedupe tool for a floor — exact matching only finds the obvious ones — or run a free CleanSmart check to see the real number, including the duplicates only semantic matching catches.