In your first year, FBA wins for anything small, light, and fast moving, and a third-party warehouse wins for oversized, slow, or bundle-heavy units. Decide per SKU rather than per brand, using fully landed cost per unit shipped. Most first-year sellers should start on FBA and add a 3PL as a reserve.
The short version
- Decide SKU by SKU. One catalog can run half on FBA and half on a 3PL with no conflict at all.
- FBA buys the Prime badge. On a listing with no review history, that badge is carrying part of your conversion rate.
- A 3PL buys cheaper storage and control. It pays off on slow movers, oversize units, kits, and anything Amazon surcharges.
- Aged inventory is where year one hurts. Stock that does not sell gets more expensive every month it sits in Amazon's network.
- The mature setup is both. A 3PL holding reserve stock and feeding FBA is standard practice, not an advanced move.
The one number that settles it
Fully landed cost per unit shipped, measured across a full replenishment cycle. Not per unit held, not per pallet, and not per shipment. Per unit that actually leaves a warehouse and reaches a customer, carrying its share of the storage you paid on the units that did not move that month.
Build it line by line. Every figure below is available to you before you commit to anything.
| Cost line | Where your number comes from | Which side it usually favors |
|---|---|---|
| Pick, pack and fulfillment per unit | Amazon's current fee schedule for your size tier, against a written 3PL quote | FBA on small and light, 3PL as units get bigger |
| Monthly storage | Seller Central storage rates, against your 3PL rate card | 3PL, and the gap widens in the fourth quarter |
| Aged inventory surcharges | Your own inventory age report | 3PL |
| Inbound freight and placement | Your forwarder's quote plus Amazon's placement charges | Whichever network sits closer to your port of entry |
| Returns handling | Bundled into FBA; billed per return by most 3PLs | FBA in categories with a high return rate |
| Delivery promise | The Prime badge, against the ship window you can promise yourself | FBA |
That last line is the one sellers leave out, and it is frequently the biggest. If moving a SKU off FBA saves sixty cents a unit and costs you two points of conversion rate, you have paid for the saving twice, once in lost orders and again in the ranking those orders would have earned.
Read the answer per SKU
- Small, light, quick to sell. Keep it in FBA. The fulfillment fee is competitive at this size, the storage exposure is small because the units turn, and the badge is worth more than the saving.
- Oversized, heavy, or slow to sell. Move it to a 3PL and ship into FBA in small, frequent batches. Oversize storage plus aged surcharges is the combination that quietly eats a first-year margin.
- Bundles, kits, multi-pack tests, and anything you also sell off Amazon. A 3PL that will assemble, relabel, and hold components gives you flexibility Amazon's network is not designed for.
- Anything under a restock limit or a stranded-inventory problem. Reserve stock outside Amazon is the only real answer, and it is worth paying for.
The reserve-stock setup most brands land on
By month six or seven, the arrangement that works looks like this: bulk inventory sits at a 3PL near your port, FBA holds about the sell-through you expect before your next inbound arrives, and you top up on a schedule tied to velocity rather than to whatever the container happened to contain. You get FBA economics on the units that move and 3PL economics on the units that wait.
Doing that well is an ongoing job rather than a one-time decision, which is why at Flapen each operator carries around 1.4 brands rather than a dozen. Restock timing, size-tier changes, and aged-stock triggers are only caught by someone close enough to the SKU to notice the trend early. When you interview any partner, ask how many brands one person handles, then ask who watches inventory age week to week. The two answers are related.
What most agencies will not tell you
Most 3PL pitches compare their pick-and-pack fee to Amazon's fulfillment fee, show a saving, and stop there. The comparison is incomplete without storage, inbound freight, returns, and the conversion effect of the badge. Ask any 3PL for a quote that models a full year including peak-season storage, then run the same year on FBA rates.
The second thing rarely said out loud: logistics is where first-year money disappears, but almost no agency contract makes anyone accountable for it. Fulfillment choices sit with you. If your candidate agency has no opinion on your size tier, your restock cadence, or your aged inventory, that is not a neutral position, it is a gap. Ask them directly what they will and will not own here, and get the answer before you sign.
Related answers
- Amazon FBA launch costs breakdown
- What to do before sending inventory to FBA
- Hidden costs in first 90 days on Amazon
- Inventory planning for Amazon Prime Day
- Amazon launch services: the complete guide
If you want a second opinion on your fulfillment mix before your next purchase order, the free written audit at Flapen covers it.
