Why Are My Shipping Rates not accurate? Too High, or Too Low?

Shipping rates are wrong! Too expensive, or not charging enough?

If customers are being undercharged or overcharged, it is usually a configuration issue in Shopify, Addition, or both. Use this guide to diagnose and fix inaccurate shipping quotes.

How Addition calculates a rate

  1. Shopify sends Addition the cart weight.
  2. Addition checks product dimensions saved in Addition to determine the most suitable package type and count.
  3. The selected package(s) and weight are sent to the carrier to return a live quote.

👉 Product dimensions must be saved in Addition. Shopify product fields and metafields are not imported. For clothing, fabric and other foldable items, enter the folded/packed size that will be shipped. Learn how to bulk edit product dimensions

Common reasons rates look too cheap or too expensive

1) Missing or incorrect dimensions in Addition

  • If a product has no dimensions in Addition, the app falls back to 5 Ă— 5 Ă— 2 cm, which can underquote.
  • Oversized or underestimated dimensions can push the quote too high or too low.

Example: A large blanket is added to Addition with dimensions entered as 100 Ă— 60 Ă— 40 cm, based on the blanket laid flat. When actually packed and compressed for shipping, the blanket only measures 40 Ă— 30 Ă— 25 cm. Because the oversized dimensions were saved, the app assumes the blanket needs a much larger box and quotes an unnecessarily expensive rate.

  • For foldable products, use folded/packed dimensions.

2) Incorrect packages configured in Addition

  • Configure all your packages in Addition > Packaging. Do not rely on Shopify package settings for Addition’s calculations.

3) Empty package weight not set

  • If your packaging alone weighs 100 g or more, set an Empty package weight in Addition. This is especially important for international quotes.

4) Discounts at checkout

  • Shopify only sends Addition the full product price (RRP) for calculations. If a discount code is applied at checkout, Addition does not see the reduced total. This can cause free shipping to trigger incorrectly or make a rate appear wrong.

5) Shopify backup rates showing instead of live rates

  • If Addition doesn’t respond within 10 seconds, Shopify can show a backup rate. These are configured in Shopify and not controlled by Addition. Learn more about Shopify backup rates

What you can check in Addition

  • Are product dimensions saved and accurate for every item, using the folded/packed size where relevant?
  • Are packages created in Addition > Packaging?
  • Have you set an Empty package weight for heavier boxes or satchels?
  • If you sell sets or multi-part items, consider setting up Product Components to model multiple cartons correctly.

What you can check in Shopify

  • Confirm every product and variant has a correct weight in Shopify.
  • Watch for unit mistakes such as entering 0.01 g instead of 0.01 kg (e.g. at 0.01 grams, Shopify rounds the weight down to zero)
  • Check for Shipping profiles that may combine rates, i.e. one shipping rate from each profile
  • Remove any old flat rates that should not appear and verify the Addition app is providing the live quote.

What rate should you expect to see?

Retail users: Compare with the Australia Post calculator

MyPost Business users: Check the latest MyPost Business Rates and Savings Guide, or login to your MyPost Business account and use the calculator

eParcel or StarTrack users: Refer to your contracted rates.

Troubleshooting checklist

  1. Was a discount code applied at checkout?
  2. Do all items have accurate folded/packed dimensions in Addition?
  3. Is an Empty package weight set if needed?
  4. Did Shopify show a backup rate instead of a live rate?
  5. Are any Shipping profiles combining rates?
  6. Do product weights and units look correct in Shopify?

Still stuck? Contact us!

If all else fails, contact support with:

  • The names and SKUs of all items in the cart, or a direct URL link to the cart
  • The total cart weight
  • The package dimensions or flat rate package size that you would ship the order in
  • The customer’s destination postcode and country
  • The rate you expected to see
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