Duty deferral is the most fundamental benefit of a Foreign Trade Zone. Instead of paying customs duties when goods arrive at the port, duties are deferred until goods leave the zone and enter U.S. commerce. The savings come from the time value of money: cash that would otherwise be tied up in duty payments stays in your business. Here is how to calculate what that is worth.

The Basic Formula

Duty deferral savings are calculated as:

For example, if your company:

• Pays $2,000,000 in annual customs duties
• Holds imported inventory an average of 90 days before it enters commerce
• Has a cost of capital of 8%

Then:

This is the cash flow benefit of not tying up $2 million in duty payments 90 days earlier than necessary. The longer the holding period and the higher your cost of capital, the greater the benefit.

Determining Your Average Holding Period

The average holding period is the time between when goods would normally be entered (at the port) and when they actually leave the FTZ for domestic consumption. This is not the same as your total inventory days. You need to measure the specific period during which duties would have been owed but are instead deferred.

To calculate it:

• For warehousing operations: Average time goods sit in the zone before being withdrawn for domestic sale. This is typically your average inventory turnover period for imported goods.
• For manufacturing operations: Time from when components arrive at the zone through manufacturing and until finished products are withdrawn for sale. This includes raw material staging, production time, and finished goods inventory.
• For distribution operations: Time from receipt at the zone to shipment to domestic customers.

Accounting for Re-Exports

Goods that are re-exported from the zone never incur duties at all. This is not a deferral; it is a complete duty elimination. For companies that re-export a portion of their imports, this benefit should be calculated separately:

If 20% of your $2,000,000 duty spend is on goods that are ultimately re-exported, that is $400,000 in full duty elimination, which is far more valuable than the deferral benefit alone.

Including MPF Consolidation

Merchandise Processing Fees (MPF) are charged at 0.3464% of the entered value, with a minimum of $31.67 and a maximum of $614.35 per entry. In an FTZ, entries can be consolidated on a weekly basis rather than per-shipment. If you file 50 individual entries per week, you pay up to $614.35 per entry ($30,717.50/week). Consolidated as a single weekly entry, the maximum is $614.35 total.

For high-volume importers, MPF consolidation savings alone can justify an FTZ.

What Data You Need

To run this calculation on your actual imports, you need:

• 12 months of entry summary data (HTS codes, duty rates, entered values)
• Average inventory holding periods for imported goods
• Re-export volume (percentage of imports that are re-exported)
• Number of entries filed per week
• Your company's cost of capital or weighted average cost of capital (WACC)

Impor can process your entry data directly from uploaded 7501 forms, spreadsheets, or PDF entry packages and run these calculations automatically with live tariff rates.

Beyond Deferral: Inverted Tariff Savings

Duty deferral is only part of the picture. For manufacturers, inverted tariff savings (paying the lower finished-product rate instead of higher component rates) are often the largest FTZ benefit. A complete FTZ cost-benefit analysis should evaluate both. See our guide on FTZ benefits by industry for examples of inverted tariff opportunities.