Distinguish one order from two items
A fixed payment fee is often attached to a transaction, while other charges may attach to a listing, unit or shipment. Putting two products in one order therefore does not automatically remove every fixed cost. Identify what actually triggers each fee before estimating a bundle saving.
This article uses a deliberately simplified schedule of 3% plus $0.30 per payment. It assumes one payment per order and no separate per-item fee. A real marketplace can add rules that make the result different. Use the schedule for your account rather than treating the example as a universal bundle benefit.
Compare equal revenue first
Two separate $20 payments incur $0.90 each under the example schedule, for $1.80 in total fees. One $40 payment incurs $1.50. The saving is $0.30: one fixed payment charge. Percentage fees are unchanged because total revenue is still $40.
This comparison only applies when the customer would otherwise make two payments. If two items were already purchased together in one checkout, merely calling them a bundle would not create an additional payment-fee saving. That distinction prevents a packaging decision from being credited with a saving that already existed.
Add the discount and fulfillment effect
Now suppose the bundle sells for $38 instead of $40. Its fee is $1.44, compared with $1.80 across the two original payments. The fee saving is $0.36, but revenue falls by $2. Before other changes, contribution is therefore $1.64 lower.
If shipping and packaging cost $1 less for the bundle, the remaining contribution reduction is $0.64. If the larger package instead costs more to ship, the outcome worsens. Check weight bands, packaging needs and picking time instead of assuming combined shipping is always cheaper.
Test the whole offer
For a bundle in the e-commerce calculator, enter the total bundle price and combined product cost. Use the actual fulfillment cost for the combined package, not automatically twice the single-item amount. Include advertising on the same basis as your comparison orders. Model any separate per-item charges explicitly within your cost assumptions.
Also consider what happens if only one part of a bundle is returned or unavailable. Those operational questions can matter more than a small fixed-fee saving. Keep the original and bundle breakdowns together, state the number of payments assumed, and evaluate the offer on its total contribution rather than the apparent reduction in one fee line.