Calculating tariffs and shipping to the US from the UK

Technical Q&A

Topic summary

A UK merchant shipping to the US via Royal Mail is encountering tariff calculation errors in Shopify following the end of the de minimis exemption on August 29. The executive order creates two systems: postal shipments should only pay the 10% IEEPA flat tariff, while commercial carriers (like FedEx) must pay both IEEPA tariff plus HS-code-specific duties.

The core problem: Shopify’s customs calculator incorrectly applies both the 10% IEEPA tariff and additional HS-code duties to all shipments, regardless of carrier type. This affects checkout calculations, Royal Mail Click & Drop integration, and commercial invoice generation.

Shopify’s response: They’ve acknowledged the issue and confirmed their calculator uses the “commercial method” for all shipments instead of distinguishing postal from commercial carriers. Developers have been notified, but no timeline for a fix was provided.

Suggested workarounds:

  • Third-party duty apps (Avalara, FlavorCloud) with override capabilities
  • Custom scripts for Shopify Plus users to apply flat 10% surcharge
  • Manual configuration of invoice/shipping apps

Additional issue reported: One merchant notes Shopify is charging 95-100% duty on certain items instead of the correct 3.5-5%.

The discussion remains open as merchants await a platform-level solution.

Summarized with AI on October 25. AI used: claude-sonnet-4-5-20250929.
1

I’ve been doing some dry run testing to prep for shipping to the usa after the end of de minimis. We have been shipping to the US for years and they are about 70% of our business. There are 3 main things I need to do - (1) calculate and collect the right duty in the store at the time of ordering, (2) transfer the order to royal mail click and drop (OBA) with the correct tariff values and (3) print our commercial invoices using a shopify linked ap and, again, the correct tariff values. The executive order that instructed the end of de minimis is pretty clear that when shipments using the mail system that would previously have met the de minimis threshold will only have to pay the ieepa tariff and not any additional duties, and so my dry run orders should have a flat 10% added before shipping. i’m using the shopify customs calculator and it is adding duties on top of this 10% that match the HS code of my products. i.e. it is incorrectly calculating the tariff, messing up all 3 of the things i need to do (above) to be able to start shipping to the us again. Is anyone else seeing this issue and is there a fix or a work around that anyone can recommend please?

1 Like
2

We’re seeing the same problem. Since the U.S. officially ended the de minimis exemption on Aug 29, every shipment must now pay the new IEEPA flat tariff plus any applicable HS-code duties. That’s why Shopify’s customs calculator is stacking both – it’s technically correct under the new rules, even though it feels like double charging.

If you only want to collect a flat 10% at checkout, you’ll need a workaround:

  • Use a duty app like Avalara or FlavorCloud that supports overrides.

  • On Shopify Plus, create a script to apply a custom 10% surcharge instead of the auto-calculated duties.

  • Or configure your invoice/shipping app to use a flat rate when passing tariff values to Royal Mail Click & Drop.

Shopify and most shipping apps are still catching up with the rule change, so updates are likely. For now, the best approach is either a duty app that understands IEEPA tariffs or a manual override until platforms add official support.

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3

The exec order kept it simpler for postal orders, so if you ship, say, FedEx then yes it’s tariff plus duties, but if you ship mail service it’s tariff only. For now at least. Thx for the solutions options, but I’m hoping I can get Shopify to fix it.

4

We’re seeing the same problem. Since the U.S. officially ended the de minimis exemption on Aug 29, every shipment must now pay the new IEEPA flat tariff plus any applicable HS-code duties. That’s why Shopify’s customs calculator is stacking both – it’s technically correct under the new rules, even though it feels like double charging.

If you only want to collect a flat 10% at checkout, you’ll need a workaround:

  • Use a duty app like Avalara or FlavorCloud that supports overrides.

  • On Shopify Plus, create a script to apply a custom 10% surcharge instead of the auto-calculated duties.

  • Or configure your invoice/shipping app to use a flat rate when passing tariff values to Royal Mail Click & Drop.

Shopify and most shipping apps are still catching up with the rule change, so updates are likely. For now, the best approach is either a duty app that understands IEEPA tariffs or a manual override until platforms add official support.

5

We are also testing it right now (UK shop too). Shopify is calculating our tariffs correctly BUT for the few items that have duties applied, it is charging 95-100% of price instead of the 3.5 - 5% duty. Other calculators are calculating them correctly but not Shopify. Will write to them but they will probably just say that their calculator is just an estimator …

6

Here’s where i got to with Shopify - at least they acknowledge the problem…

“Here is what I’ve found:

  • The new U.S. executive order created a two-tiered system. For a limited transition period, commercial carriers and postal services are handling the new tariffs differently.

  • Your carrier, Royal Mail, is using the postal service’s method. This method, for countries like the UK, primarily charges the 10% IEEPA tariff, not the additional duties based on a product’s HS code.

  • Shopify’s calculator is using the commercial method. Our built-in calculator, which relies on a third-party partner’s algorithm, is currently treating all international shipments as if they are commercial, which is why it’s adding the HS code-related duty and showing a total of 15.6%.

The result is a direct conflict between what is calculated at your checkout and what your carrier will actually charge. As you correctly pointed out, this could lead to both a poor customer experience and issues with customs.

I have informed our developers to advise them about this. I also want to assure you that you are not the only merchant experiencing this, and our team is working to align our calculator with the new postal rules.

While I cannot provide a timeline for a permanent fix, I can provide you with the following immediate options:”

And then they went on to suggest the usual bs solutions, like use an ap that costs 10x what i’m paying for shopify just to add put a line item on the checkout that is 10% of the subtotal…