Ecommerce Funnel Calculator: Where Are You Losing Sales?

Bring one consistent, closed funnel

Enter unique sessions or unique users that completed each step in order: entry, cart, checkout, purchase. Pick one unit for all four counts, one population and one observation window. Counts must be whole numbers from zero to 100 million and must never increase down the funnel. Do not paste raw event counts or combine Shopify sessions with GA4 users. A user or session with several orders counts once in this model; contribution should therefore be per extra converting unit, not automatically per order.

Enter a recovery assumption from 0 to 100 percent and contribution from zero to one million currency units, each with at most two decimal places. Contribution should deduct relevant variable costs, including your declared returns allowance; implementation and experiment costs remain separate. All financial values use one currency. The anonymous scope note is retained only in your local export, not sent as analytics.

How each scenario is calculated

For each adjacent transition, drop-offs = entered − advanced. Step completion = advanced ÷ entered. Recovering r of the drop-offs gives extra advances = drop-offs × r. Holding downstream behavior fixed, extra purchasing units = extra advances × current purchases ÷ current advanced units. Extra contribution = extra purchasing units × contribution per converting unit.

These are three separate one-change scenarios. They are not additive because changing an earlier transition also changes the population eligible for later steps. The final transition has downstream completion 1 when purchases exist. If there have been no advanced units, the downstream rate is unobserved: positive recovery cannot be valued. Zero recovery always yields zero extra contribution. An empty entry cohort has no defined conversion rate.

Check the example by hand

10,000 entries → 1,000 carts → 600 checkouts → 300 purchases gives step completion of 10%, 60% and 50%. At 10% recovery, additional advances are 900, 40 and 30. Downstream completion is 30%, 50% and 100%, giving 270, 20 and 30 extra converting units. At contribution 30, the results are 8,100, 600 and 900. Every number is synthetic. Decimal results are expected values under the scenario, not literal fractions of people.

Use the result to prioritize investigation

Rerun at a lower recovery assumption and compare the implied contribution with the implementation cost over the same period. A positive figure does not approve the project. Check whether the friction is reproducible, whether the intervention can plausibly affect that transition and whether additional buyers have comparable economics. Do not call the result lost revenue, causal lift, a forecast or a confidence interval.

The calculator deliberately rejects open-funnel counts that increase, but monotonic counts alone cannot prove a closed cohort. Verify the underlying sequence before entering data. Copy or download the full review to retain input definitions and limitations. Editing any field clears stale results, and reset restores the synthetic numbers.

Sources and limitations

Primary documentation checked October 18, 2026: Shopify behavior reports explains session-based open and closed funnels; Google Analytics funnel exploration explains user-based sequence counting. Publication dates are unknown for these living documents. These systems do not automatically share a denominator. The worksheet and scenario method are original editorial synthesis, not vendor-approved benchmarks. Examples are synthetic, not client results.