Amazon Arbitrage Minimum Prices: How to Set Your Floor and Never Sell Below Cost

Last updated: September 2026

Every arbitrage seller who has repriced without a correctly calculated minimum price has sold at least one unit below cost. The repricer did exactly what it was configured to do. The configuration was wrong.

The minimum price in a repricer is the only barrier between a competitive pricing event and a margin-negative sale. If a competitor drops their price to below your break-even, a repricer without a correctly calculated floor follows them. One with a correct floor holds. The difference is the formula you used to calculate the minimum, and whether it included all the cost components that make arbitrage different from wholesale.

TL;DR: The floor formula for Amazon arbitrage is: (sourcing cost + prep cost + FBA fee) divided by (1 minus referral fee rate minus target margin rate). The result is the lowest price that protects your target margin on that specific lot. In arbitrage, each lot has a different floor because each lot has a different sourcing cost. Set the minimum per ASIN to the higher of: the floor from your most expensive active lot, or the MAP price if one applies. Safe Mode confirms the configuration before any live prices change.

Why arbitrage sellers are most at risk from incorrect minimum prices

Arbitrage sellers face a specific repricing risk that wholesale and private label sellers do not: their sourcing cost varies by deal, by lot, and sometimes by unit within the same ASIN. A floor that is correct for one lot is wrong for the next if sourcing costs differ.

Wholesale sellers typically pay a consistent per-unit cost from a single supplier. Private label sellers pay a fixed manufacturing cost that changes only when they renegotiate or switch manufacturers. Both models allow a relatively stable floor per ASIN that needs updating infrequently.

Arbitrage is different. A retail arbitrage (RA) seller might source 20 units of the same ASIN at a clearance price of $4.99 in February and 30 units at the regular retail price of $7.99 in April. These two lots have two different floors. A single minimum price set in the repricer is accurate for one of them and wrong for the other.

The second risk specific to arbitrage is prep cost. RA and OA sellers typically pay for labelling, polybag, bubble wrap, or prep centre processing costs per unit. These costs are small individually but compound to a meaningful floor difference when excluded. A floor calculated without prep costs is systematically understated.

The third risk is using Amazon's Automate Pricing with an estimated minimum rather than a calculated one. Typing a round number into the minimum field because it "seems about right" is the most common origin story for below-cost sales in arbitrage.

The complete minimum price formula: every cost component

The floor formula produces the minimum price at which a specific unit produces at least the target margin percentage. Every component is required. Estimating or omitting any one of them produces an inaccurate floor.

The formula:

Floor = (sourcing cost + prep cost + FBA fee) divided by (1 minus referral fee rate minus target margin rate)

Each component:

Sourcing cost: The price paid per unit at the point of sourcing, including any applicable taxes if not recoverable. For OA, this is the retailer's price including shipping to your location. For RA, this is the in-store price. Not the MSRP. Not the retail sticker price if you paid a different amount.

Prep cost: The per-unit cost of preparing the item for FBA. This includes: FNSKU barcode labels (printed or purchased), polybag if required for the category, bubble wrap for fragile items, and prep centre fees if you outsource this step. Typical prep costs run $0.30 to $2.00 per unit depending on what is required. This cost is frequently omitted from floor calculations and silently reduces margin on every unit.

FBA fulfillment fee: Amazon's per-unit pick, pack, and ship charge based on the product's size tier and weight. Use the Revenue Calculator in Seller Central for the specific ASIN to get the correct fee. Do not estimate. The January 2026 FBA fee update changed rates for multiple size tiers. Any floor calculated before January 15, 2026 on affected tiers is potentially understated. Current fee inputs are in the Amazon seller fees guide.

Referral fee rate: Amazon's category commission percentage, applied to the selling price. Rates vary from 8% to 15% depending on category. Confirm the referral fee for the specific category in Seller Central rather than using a category average.

Target margin rate: The net margin percentage you want to achieve per unit. For arbitrage, 15% to 25% is a common target range depending on category and sourcing model. This is a business decision, not a cost. Set it explicitly in the formula.

Worked example: sourcing cost + prep + fee + margin = your floor

This example uses realistic numbers for a typical RA find. Apply the same formula to every ASIN in your arbitrage catalogue, using the actual costs for each product.

Product: Home goods item sourced at a chain retailer

Floor = $10.67 divided by 0.72 = $14.82

Every unit of this product must sell at or above $14.82 to produce at least 20% net margin after all costs.

Verification:

At $14.82 selling price:

• Referral fee (8%): $1.19

• FBA fee: $3.18

• Prep cost: $0.50

• Sourcing cost: $6.99

• Total costs: $11.86

• Net profit: $14.82 minus $11.86 = $2.96

• Margin: $2.96 divided by $14.82 = 20.0%

The formula holds. Any price above $14.82 on this lot produces more than 20% margin. Any price below it produces less than 20% or a loss.

Common floor calculation errors in arbitrage:

Forgetting prep costs underestimates the floor. On this product, omitting the $0.50 prep cost produces a floor of $14.13 instead of $14.82. At $14.13 with $0.50 prep cost included, the actual margin is 16%, not 20%. Across 200 units sold at $14.13 rather than $14.82, that is $138 in missing margin from a single overlooked cost component.

Start your 14-day free trial with Safe Mode. Enter your calculated floors for each ASIN and run the simulation for 7 days before any live prices change.

How to handle per-lot sourcing cost variation

When you source the same ASIN at two different prices in two different lots, you have two different floors for the same product. This is the characteristic repricing challenge of arbitrage, and handling it correctly determines whether your minimum price protects all of your inventory.

The scenario:

• Lot 1: 20 units sourced at $6.99. Floor = $14.82 (from the worked example above)

• Lot 2: 30 units sourced at $8.49. Floor calculation: ($8.49 + $0.50 + $3.18) divided by 0.72 = $12.17 divided by 0.72 = $16.90

Both lots are active in FBA simultaneously. The repricer has one minimum price setting for the ASIN.

Option 1: Set the floor to the higher lot's floor ($16.90)

This protects all inventory. Every unit sold, from either lot, is sold above the floor of the more expensive lot. Lot 1 units sell with higher margin than intended (bonus margin). Lot 2 units are protected at their correct floor.

The trade-off: at $16.90 minimum, you lose Buy Box to competitors who price between $14.82 and $16.89. Lot 1 inventory that would sell competitively at $14.82 to $16.89 is held at $16.90 or higher.

Option 2: Set the floor to the lower lot's floor ($14.82)

This captures competitive pricing on Lot 1 but leaves Lot 2 exposed. At any price between $14.82 and $16.90, the Lot 2 units sell below their floor, producing less than 20% margin. The amount depends on how far below $16.90 the price goes.

Option 3: Use an OA sourcing tool integration to pass per-lot costs to Repricer.com

For sellers using OAGenius or ArbitrageBoss, the Repricer.com integrations allow per-lot sourcing cost data to pass directly from the sourcing tool to Repricer.com's floor calculation. When a new lot at $8.49 is logged in OAGenius, the updated floor propagates to Repricer.com without manual entry. This is covered in detail in the online arbitrage repricing guide.

Option 4: Average cost approach

If both lots are small and will turn over quickly, calculate the weighted average cost across lots: ((20 × $6.99) + (30 × $8.49)) divided by 50 = ($139.80 + $254.70) divided by 50 = $394.50 divided by 50 = $7.89 average cost. Floor at $7.89 sourcing cost: ($7.89 + $0.50 + $3.18) divided by 0.72 = $11.57 divided by 0.72 = $16.07.

The average cost floor protects most inventory at most prices without requiring per-lot tracking. It is less precise than per-lot floors but simpler to maintain for sellers without tool integrations.

The conservative recommendation for new arbitrage repricers:

Until per-lot floor management is set up with tool integrations, use the highest-cost lot's floor as the minimum. Protect all inventory at the highest floor rather than risk below-floor sales on any lot. The margin sacrificed on cheaper lots is less costly than the margin lost on below-floor sales.

Setting minimum prices in Repricer.com for per-ASIN sourcing costs

Every ASIN in an arbitrage catalogue needs its own minimum price calculated from its specific costs. A blanket minimum across the catalogue does not reflect per-ASIN cost variation and will overprotect low-cost ASINs and underprotect high-cost ones.

Per-ASIN minimum price entry:

In Repricer.com, the minimum price is set per ASIN or SKU. For each active arbitrage ASIN:

1. Calculate the floor using the formula above with the actual costs for that ASIN

2. Enter the calculated floor as the minimum price for that ASIN

3. Set the maximum price (ceiling) from Keepa's 90-day Buy Box price historical high

4. Select the rule type based on competitive density (match for 4+ FBA sellers, ceiling-hunt for 1 to 2)

Bulk minimum price updates:

For catalogues with dozens or hundreds of arbitrage ASINs, entering minimum prices individually is time-consuming. Repricer.com supports bulk minimum price import via CSV. Prepare a spreadsheet with ASIN, calculated floor, and ceiling for each product, then upload. This is particularly efficient after a sourcing run where multiple new ASINs need floor entries before repricing.

The floor update trigger:

Minimum prices need updating when:

• A new lot of the same ASIN arrives at a different sourcing cost (update to higher-lot floor per the recommendation above)

• Amazon changes FBA fees (the January 2026 increase affected multiple standard size tiers)

• The referral fee rate changes for the category

• The target margin is adjusted for the business

The 10-point repricing configuration audit catches floor accuracy issues systematically and is the correct tool for verifying floors across an arbitrage catalogue after any of these triggers.

What to do when competitor prices fall below your floor

When a competitor's price falls below your minimum, Repricer.com holds at your floor. You lose Buy Box to the competitor at the lower price. This is the correct outcome. The minimum price exists precisely to prevent selling below cost regardless of competitive pressure.

The decision not to follow:

Lowering your floor to follow a competitor below your break-even is selling at a loss. The short-term cost of losing Buy Box to a below-cost competitor is less than the cost of selling your entire remaining lot at a margin-negative price. A temporarily suppressed Buy Box recovers when the competitor's stock depletes or they correct their pricing. A below-floor sale is permanent.

What typically happens when competitors fall below floor:

In most cases, a competitor pricing below the sustainable floor for a product is operating on either an incorrect floor of their own (not accounting for all costs) or liquidating unsustainable inventory. These situations resolve within days or weeks. Hold your floor and resume competitive Buy Box rotation when the competitor adjusts.

When to investigate rather than hold:

If your floor is significantly above the competitive price range for an extended period (more than 7 days), investigate whether your floor is correctly calculated. Three possibilities:

1. Your sourcing cost for this lot is genuinely higher than the competitive range supports at your target margin. This is a sourcing problem, not a repricing problem.

2. Your floor calculation included an error. Recalculate using the formula and verify each component.

3. The competitive price range has dropped below the level at which this product is commercially viable for FBA. Exit the ASIN.

The profit-first repricing guide covers the framework for deciding when to hold a floor, when to lower a target margin to remain competitive, and when to exit an ASIN entirely.

Using Safe Mode to test your minimums before going live

Safe Mode runs Repricer.com against your live listings without changing any prices. For arbitrage sellers with newly entered floors, this 7-day simulation confirms that the minimum prices are set correctly and that the repricer produces better outcomes than your current approach before any live prices change.

The Safe Mode confirmation process for arbitrage floors:

1. Enter the calculated floor for each active ASIN using the formula above

2. Set the ceiling from Keepa's 90-day historical high

3. Enable Safe Mode on all active repricing ASINs

4. After 7 days, compare the simulated average selling price to your actual average selling price from Seller Central Business Reports

5. Check for floor breach events in the Safe Mode report: any time the simulated rule tried to go below the floor indicates the competitive range fell below your minimum on that ASIN

What floor breach events mean:

A high number of floor breach events on a specific ASIN indicates the competitive price range is frequently at or below your minimum. This is not a Safe Mode problem. It signals that the market price for this ASIN is close to your break-even. Investigate whether the sourcing cost for this lot is too high for the current competitive range, or whether the competitive range has declined below the sustainably profitable level.

When to go live:

If the simulated average selling price is higher than your actual average selling price during the same 7-day period at comparable Buy Box share: go live. The configuration is confirmed to produce better outcomes.

If the simulated ASP is lower: investigate the configuration before enabling. Common causes in arbitrage: minimum set too high (above the competitive range), ceiling set below the current competitive price, rule type mismatch for the competitive density.

Key Takeaways

• The floor formula for arbitrage: (sourcing cost + prep cost + FBA fee) divided by (1 minus referral fee rate minus target margin rate). Every component is required. Omitting prep costs or using estimated FBA fees produces an inaccurate floor.

• Per-lot cost variation is the characteristic arbitrage repricing challenge. When two lots of the same ASIN have different sourcing costs, they have different floors. Set the minimum to the higher-lot floor to protect all inventory without tracking per-lot exposure.

• The minimum price is the only barrier between a competitive event and a below-cost sale. A repricer holds at the minimum regardless of competitive pressure. Lowering the minimum to follow a competitor below cost is selling at a loss.

• Arbitrage sellers using OAGenius or ArbitrageBoss should connect these tools to Repricer.com via the integrations page. Per-lot cost data passes automatically, removing the manual floor update burden after each sourcing run.

• Safe Mode confirms the configuration before any live prices change. Run for 7 days after entering floors. Check floor breach events. Go live when the simulation produces a higher simulated ASP than your actual ASP over the same period.

Action Plan

1. List every active arbitrage ASIN in your current catalogue. For each one, identify the sourcing cost from the most expensive active lot.

2. Pull the FBA fee for each ASIN from the Revenue Calculator in Seller Central. Do not estimate. Use the current fee schedule post-January 2026.

3. Confirm prep cost per ASIN. If you use a prep centre, get the per-unit rate. If you prep at home, estimate honestly: label cost, polybag if required, time cost if billing yourself at a rate.

4. Calculate the floor for each ASIN: (sourcing cost + prep cost + FBA fee) divided by (1 minus referral fee rate minus target margin rate). Record these in a spreadsheet.

5. Enter the calculated floors as minimum prices in Repricer.com. For ASINs with multiple active lots at different costs, use the higher-lot floor.

6. Set ceilings from Keepa: the 90-day Buy Box price historical high per ASIN.

7. Enable Safe Mode for 7 days. Review floor breach events and simulated ASP vs actual ASP at the end of the 7-day period.

8. Go live when Safe Mode confirms better simulated outcomes. After enabling, run the 10-point repricing audit monthly for the first quarter to catch any floor accuracy issues from new lots.

Frequently Asked Questions

1. How do I set minimum prices for my Amazon arbitrage products?

Use the floor formula: (sourcing cost + prep cost + FBA fee) divided by (1 minus referral fee rate minus target margin rate). For each ASIN, substitute your actual costs: the price paid for the sourcing lot, the per-unit prep cost (labelling, polybag, prep centre fee), the FBA fulfillment fee from Amazon's Revenue Calculator, the referral fee percentage for the category, and your target margin percentage. The result is the minimum price for that lot. Enter this as the minimum price per ASIN in Repricer.com. For multiple active lots at different sourcing costs, use the higher-lot floor as the minimum.

2. What is the formula for calculating a minimum repricing price?

Floor = (sourcing cost + prep cost + FBA fee) divided by (1 minus referral fee rate minus target margin rate). For a product sourced at $6.99 with $0.50 prep cost, $3.18 FBA fee, 8% referral fee, and 20% target margin: ($6.99 + $0.50 + $3.18) divided by (1 minus 0.08 minus 0.20) = $10.67 divided by 0.72 = $14.82. This produces exactly 20% net margin at the minimum price. Prices above $14.82 on the same product produce higher margin.

3. How do I make sure my repricer never sells below cost?

Set the minimum price in Repricer.com to the calculated floor from the formula above. The repricer holds at this minimum regardless of competitive events. If a competitor prices below your floor, the repricer does not follow. You temporarily lose Buy Box to the competitor but do not sell below cost. The two conditions that cause below-cost sales are: no minimum price set (the repricer has no lower bound), or a minimum price set below the true break-even (from omitting prep costs, using incorrect FBA fees, or not accounting for the referral fee correctly). Verify all three inputs before setting any minimum.

4. What happens if all competitor prices fall below my minimum?

The repricer holds at your minimum. You lose Buy Box to competitors pricing below your floor. This is commercially correct: selling below the calculated floor produces below-target margin or a loss, regardless of how many units you sell. In most cases, competitors pricing below a product's sustainable floor correct their pricing or deplete their inventory within days to weeks. The practical response is to hold the floor, check whether the competitive range decline indicates a structural problem with the sourcing (too high a cost for the current market), and decide whether to source more of this ASIN at the current price range before evaluating further.

Start your 14-day free trial with Safe Mode. Enter your calculated floors for every arbitrage ASIN. See the Repricer.com features page for the full minimum price configuration options including bulk import and per-SKU settings.