diff --git a/documentation/properties/period.md b/documentation/properties/period.md
new file mode 100644
index 00000000..7039af42
--- /dev/null
+++ b/documentation/properties/period.md
@@ -0,0 +1,48 @@
+---
+layout: property
+title: "period"
+schemas:  [exchange_rate]
+---
+
+# period
+
+---
+
+
+
+# Exchange Rate
+
+The period corresponds to the methodology and period over which the excange rate has been calculated. This assumes that the current **date** is the end of the period. So *avg_3m* can be understood as the average rate over the past 3 months.
+
+If period is blank, it can be assumed the that rate corresponds to the current spot rate (ie. no period). The spot rate is the reference rate that corresponds to the exchange rate on the provided **date**. Reference rates are rates determined by the firm or the relevant central bank for a given date for reporting purposes. (e.g. [ECB EUR Reference Rates][ecb-ref-rates], [BoE Reference Rates][boe-ref-rates]). If **type** is left blank that it can be assumed to be the spot rate for the given **date** of the data.
+
+
+```bash
+├── avg_1m
+├── avg_3m
+├── avg_6m
+├── avg_12m
+└── avg_ytd
+```
+
+
+### avg_1m
+The average rate over the past month.
+
+### avg_3m
+The average rate over the past 3 months.
+
+### avg_6m
+The average rate over the past 6 months.
+
+### avg_12m
+The average rate over the past 12 months.
+
+### avg_ytd
+The average rate since the start of the current calendar year.
+
+
+---
+
+[ecb-ref-rates]: https://www.ecb.europa.eu/stats/policy_and_exchange_rates/euro_reference_exchange_rates/html/index.en.html
+[boe-ref-rates]: https://www.bankofengland.co.uk/statistics/exchange-rates
diff --git a/documentation/properties/purpose.md b/documentation/properties/purpose.md
index 505e8826..aa6ef669 100644
--- a/documentation/properties/purpose.md
+++ b/documentation/properties/purpose.md
@@ -953,7 +953,6 @@ In the context of [CRR][crr] Article 328, a reference security would be the unde
 ### share_capital
 This indicates shares that have been [issued][issued] for the purpose of raising capital for the company.
 
-[issued]: https://www.investopedia.com/terms/s/sharecapital.asp
 
 ### non_controlling
 [Commission Regulation (EC) No 494/2009][reg] defines **non-controlling interest** as:
@@ -968,14 +967,14 @@ Use this enumeration value to highlight back to back trades defined as "exactly
 ### single_collateral_pool
 Use this enumeration value to identify to securities which are placed into a central bank single collateral pool. A list of eligible security types for the Bank of England SCP can be found [here][scp]
 
-[scp]: https://www.bankofengland.co.uk/markets/eligible-collateral
 
 ### ocir
 Use this enum to refer to funds reserved for the purpose of implementing, from an operational point of view, the resolution strategy and, consequently, to stabilise and restructure the bank.
 
 [Bank of England OCIR][ocir]
 
-[ocir]: https://www.bankofengland.co.uk/-/media/boe/files/prudential-regulation/supervisory-statement/2021/ss421-may-2021.pdf
+
+
 
 ---
 
@@ -991,4 +990,7 @@ Use this enum to refer to funds reserved for the purpose of implementing, from a
 [osfi-bb]: https://www.osfi-bsif.gc.ca/en/data-forms/reporting-returns/filing-financial-returns/financial-reporting-instructions/irb-credit-data-wholesale-portfolio-part-1-bb
 [osfi-bd]: https://www.osfi-bsif.gc.ca/en/data-forms/reporting-returns/filing-financial-returns/financial-reporting-instructions/irb-credit-data-retail-portfolio-part-1-bd
 [osfi-b20]: https://www.osfi-bsif.gc.ca/Eng/Docs/b20_dft.pdf
+[scp]: https://www.bankofengland.co.uk/markets/eligible-collateral
+[issued]: https://www.investopedia.com/terms/s/sharecapital.asp
+[ocir]: https://www.bankofengland.co.uk/-/media/boe/files/prudential-regulation/supervisory-statement/2021/ss421-may-2021.pdf
 
diff --git a/schemas/exchange_rate.json b/schemas/exchange_rate.json
index 1a180212..2f1b24cf 100644
--- a/schemas/exchange_rate.json
+++ b/schemas/exchange_rate.json
@@ -17,6 +17,17 @@
       "description": "The base currency in accordance with ISO 4217 standards.",
       "$ref": "https://raw.githubusercontent.com/SuadeLabs/fire/master/schemas/common.json#/currency_code"
     },
+    "period": {
+      "description": "Describes the reference methodology and period for the exchange rate.",
+      "type": "string",
+      "enum": [
+        "avg_12m",
+        "avg_1m",
+        "avg_3m",
+        "avg_6m",
+        "avg_ytd"
+      ]
+    },
     "quote": {
       "description": "The amount of the quote currency received in exchange for 1 unit of the base currency.",
       "type": "number"
@@ -34,6 +45,12 @@
       "type": "string"
     }
   },
-  "required": ["id", "date", "base_currency_code", "quote", "quote_currency_code"],
+  "required": [
+    "id",
+    "date",
+    "base_currency_code",
+    "quote",
+    "quote_currency_code"
+  ],
   "additionalProperties": true
-}
+}
\ No newline at end of file
diff --git a/v1-dev/exchange_rate.json b/v1-dev/exchange_rate.json
index 1a180212..2f1b24cf 100644
--- a/v1-dev/exchange_rate.json
+++ b/v1-dev/exchange_rate.json
@@ -17,6 +17,17 @@
       "description": "The base currency in accordance with ISO 4217 standards.",
       "$ref": "https://raw.githubusercontent.com/SuadeLabs/fire/master/schemas/common.json#/currency_code"
     },
+    "period": {
+      "description": "Describes the reference methodology and period for the exchange rate.",
+      "type": "string",
+      "enum": [
+        "avg_12m",
+        "avg_1m",
+        "avg_3m",
+        "avg_6m",
+        "avg_ytd"
+      ]
+    },
     "quote": {
       "description": "The amount of the quote currency received in exchange for 1 unit of the base currency.",
       "type": "number"
@@ -34,6 +45,12 @@
       "type": "string"
     }
   },
-  "required": ["id", "date", "base_currency_code", "quote", "quote_currency_code"],
+  "required": [
+    "id",
+    "date",
+    "base_currency_code",
+    "quote",
+    "quote_currency_code"
+  ],
   "additionalProperties": true
-}
+}
\ No newline at end of file