Live Shipping Calculation Amounts Incorrect - USPS and FedEx

New Member
1 0 2

I have live carrier shipping estimates set up in Shopify for USPS (United States) and USPS and FedEx (United Kingdom), but the actual rates being quoted at checkout are not accurate (either too high or two low).

Each of our products variants specifies a weight of 8 ounces, and our default package is set at 2 ounces.

For example, I did a test order for a product (1 item/8 ounces) to ship from MI to CA.   At checkout, the USPS shipping amount for First Class came up as $2.54. However, when I compare that to the shipping rate tables for Zone 8 (MI to CA), the amount for First Class comes up at $7.15. 

Does anyone know how the live shipping rates are calculated for USPS and FedEx so I can figure out what I set up incorrectly?   I don’t need to see the code, but is there a formula so I can try to back into what is causing the errors.

The international rates are being miscalculated too (mostly they are coming up as too high), but the example above is hopefully enough to dig into and figure out what is wrong.






New Member
1 0 1

Hi Janine.

I'm having a similar issue. I just shipped a local package that Shopify estimated as $2.50, then it actually shipped (via ShipStation) for $3.60. Then... Shopify just charged a customer $13.41 for an international package, but the actual shipping there was $25.50! I thought the WHOLE POINT of carrier calculated shipping was to get accurate rates for packages. It seems to not be doing the one thing it's supposed to do!


1 Like
Shopify Staff
Shopify Staff
127 0 7

Hey there!

For the carrier calculated shipping rates that appear, they are based off of the product's weight and will choose the mail service and best price available for the packaging dimensions you have set. The locations you are sending to and from will also affect the rate displayed. These rates are taken directly real-time from the carrier.

If the product had qualified for First-Class Package Service with USPS, and had weighed 8oz and was within the eligible packaging dimensions for the service, that seems to be an accurate charge.

Click here for information on the pricing changes from USPS in Jan/16.  

I would suggest sending us an email to with a few order examples to take a closer look if you're having any further issues there. :)

Here is some more information about how carrier calculated shipping works, and how to configure it if you need to modify the pricing for handling costs or anything if required.

Hope that helps!

Justin L

170 0 10

I have a much bigger problem. Sometime in the last week or so my carrier calculated rates started charging almost double the rates that FedEx and USPS show me directly. I really hope they get this resolved soon as I'm losing sales and getting upset customers.

New Member
9 0 0

As easy as using the carrier-calculated rates theoretically is, it's been nothing but a pain to figure out. Some of the weights on a few products fluctuate from one another; for example, one brand of t-shirt weighs more/less than another, but I entered the weights based on whatever brand I had on hand at the moment. Because of this, I use the Markup percent field and raise the cost about 10%.

The one thing I can't seem to figure out is how it uses the percentage markup field. What is it basing the 10% on? Weight? Original shipping rate? Cost of the product? It appears to be completely random. Sometimes it appears to be charging double what it should cost, which is exceptionally frustrating. Nothing on Shopify appears to explain how it works either. Anyone else figure this out?

New Member
15 0 0

I have a recommendation of an app that can help you out.-Please let me know so I can pm you. Thanks

New Member
133 0 0

Hello @Janine3@Christopher_Od1,


There are two main reasons why you don't get accurate FedEx/USPS rates:

  • Package weight. Please ensure you have configured the product weight correctly.
  • Shipper address or recipient address. When the addresses are outside the serviceable area for the carrier, they charge huge surcharge for such addresses. Do verify that your addresses are within the serviceable areas.

If you are still facing the issue, please contact the carrier based on your shipper volume. Also, you can use a dedicated app like the FedEx Rates, Labels and Tracking app to automate the shipment process using your own FedEx account.


Now, if your shipping volume is low,  then you can find a shipping broker in order to get cheap rates. In this case, you will have to charge the customer Flat Rate or Free Shipping and manually fulfill the orders in Shopify.