diff --git a/.changeset/make-activity-dates-optional.md b/.changeset/make-activity-dates-optional.md
new file mode 100644
index 00000000..8532971e
--- /dev/null
+++ b/.changeset/make-activity-dates-optional.md
@@ -0,0 +1,5 @@
+---
+"@hypercerts-org/lexicon": patch
+---
+
+Make startDate and endDate optional in activity lexicon
diff --git a/ERD.puml b/ERD.puml
index e23f00ef..50349d49 100644
--- a/ERD.puml
+++ b/ERD.puml
@@ -60,8 +60,8 @@ dataclass activity <<largeBold>> #B4E5D0 {
     description?
     image?
     workScope?
-    startDate
-    endDate
+    startDate?
+    endDate?
     contributions[]?
     locations[]?
     rights?
diff --git a/README.md b/README.md
index 1a25b0d1..3a5a19aa 100644
--- a/README.md
+++ b/README.md
@@ -293,8 +293,8 @@ Hypercerts-specific lexicons for tracking impact work and claims.
 | `description`      | `string` | ❌       | Optional longer description of the impact work done.                                         |                                                                           |
 | `image`            | `union`  | ❌       | The hypercert visual representation as a URI or image blob                                   |                                                                           |
 | `workScope`        | `object` | ❌       | Logical scope of the work using label-based conditions                                       | Object with `withinAllOf`, `withinAnyOf`, `withinNoneOf` arrays of labels |
-| `startDate`        | `string` | ✅       | When the work began                                                                          |                                                                           |
-| `endDate`          | `string` | ✅       | When the work ended                                                                          |                                                                           |
+| `startDate`        | `string` | ❌       | When the work began                                                                          |                                                                           |
+| `endDate`          | `string` | ❌       | When the work ended                                                                          |                                                                           |
 | `contributions`    | `array`  | ❌       | A strong reference to the contributions done to create the impact in the hypercerts          | References must conform to `org.hypercerts.claim.contribution`            |
 | `rights`           | `ref`    | ❌       | A strong reference to the rights that this hypercert has                                     | References must conform to `org.hypercerts.claim.rights`                  |
 | `locations`        | `ref`    | ❌       | An array of strong references to the locations where the work for done hypercert was located | References must conform to `app.certified.location`                       |
diff --git a/lexicons/org/hypercerts/claim/activity.json b/lexicons/org/hypercerts/claim/activity.json
index d0b2c45b..7e702984 100644
--- a/lexicons/org/hypercerts/claim/activity.json
+++ b/lexicons/org/hypercerts/claim/activity.json
@@ -8,13 +8,7 @@
       "key": "any",
       "record": {
         "type": "object",
-        "required": [
-          "title",
-          "shortDescription",
-          "createdAt",
-          "startDate",
-          "endDate"
-        ],
+        "required": ["title", "shortDescription", "createdAt"],
         "properties": {
           "title": {
             "type": "string",