diff --git a/api-specs/api/types/cart/ExternalTaxRateDraft.raml b/api-specs/api/types/cart/ExternalTaxRateDraft.raml
index 8d6f319ea..41f9b8efe 100644
--- a/api-specs/api/types/cart/ExternalTaxRateDraft.raml
+++ b/api-specs/api/types/cart/ExternalTaxRateDraft.raml
@@ -36,4 +36,4 @@ properties:
   subRates?:
     type: SubRate[]
     description: |
-      For countries (such as the US) where the total tax is a combination of multiple taxes (such as state and local taxes).
+      For countries (such as the US) where the total tax is a combination of multiple taxes (such as state and local taxes). The total of all subrates must equal the TaxRate `amount`.
diff --git a/api-specs/api/types/tax-category/TaxRate.raml b/api-specs/api/types/tax-category/TaxRate.raml
index c210e6d80..00dedc637 100644
--- a/api-specs/api/types/tax-category/TaxRate.raml
+++ b/api-specs/api/types/tax-category/TaxRate.raml
@@ -26,7 +26,7 @@ properties:
     minimum: 0
     maximum: 1
     description: |
-      Tax rate. If subrates are used, the amount must be the sum of all subrates.
+      Tax rate. If subrates are used, the amount is the sum of all rates in `subRates`.
   includedInPrice:
     type: boolean
     description: |
@@ -42,4 +42,4 @@ properties:
   subRates?:
     type: SubRate[]
     description: |
-      Used to calculate the [taxPortions](/../api/projects/carts#taxedprice) field in a Cart or Order. It is useful if the total tax of a country (such as the US) is a combination of multiple taxes (such as state and local taxes).
+      Used to calculate the [taxPortions](/../api/projects/carts#taxedprice) field in a Cart or Order. It is useful if the total tax of a country (such as the US) is a combination of multiple taxes (such as state and local taxes). The total of all subrates equals the TaxRate `amount`.
diff --git a/api-specs/api/types/tax-category/TaxRateDraft.raml b/api-specs/api/types/tax-category/TaxRateDraft.raml
index 01052d775..f4ee512a4 100644
--- a/api-specs/api/types/tax-category/TaxRateDraft.raml
+++ b/api-specs/api/types/tax-category/TaxRateDraft.raml
@@ -29,7 +29,7 @@ properties:
   subRates?:
     type: SubRate[]
     description: |
-      Used to calculate the [taxPortions](/../api/projects/carts#taxedprice) field in a Cart or Order. It is useful if the total tax of a country (such as the US) is a combination of multiple taxes (such as state and local taxes).
+      Used to calculate the [taxPortions](/../api/projects/carts#taxedprice) field in a Cart or Order. It is useful if the total tax of a country (such as the US) is a combination of multiple taxes (such as state and local taxes). The total of all subrates must equal the TaxRate `amount`.
   key?:
     type: string
     description: |