diff --git a/changelogs/unreleased/50559-add-milestone-progress-to-api.yml b/changelogs/unreleased/50559-add-milestone-progress-to-api.yml
new file mode 100644
index 00000000000..e68e4bd6059
--- /dev/null
+++ b/changelogs/unreleased/50559-add-milestone-progress-to-api.yml
@@ -0,0 +1,5 @@
+---
+title: 'API: Expose milestone progress'
+merge_request: 25173
+author: Robert Schilling
+type: added
diff --git a/doc/api/group_milestones.md b/doc/api/group_milestones.md
index 7be01ce9c6d..920acaf3e49 100644
--- a/doc/api/group_milestones.md
+++ b/doc/api/group_milestones.md
@@ -42,6 +42,7 @@ Example Response:
     "due_date": "2013-11-29",
     "start_date": "2013-11-10",
     "state": "active",
+    "percentage_complete" : 66,
     "updated_at": "2013-10-02T09:24:18Z",
     "created_at": "2013-10-02T09:24:18Z"
   }
diff --git a/doc/api/milestones.md b/doc/api/milestones.md
index fa8f8a0bcf0..21a390442bd 100644
--- a/doc/api/milestones.md
+++ b/doc/api/milestones.md
@@ -39,6 +39,7 @@ Example Response:
     "due_date": "2013-11-29",
     "start_date": "2013-11-10",
     "state": "active",
+    "percentage_complete" : 66,
     "updated_at": "2013-10-02T09:24:18Z",
     "created_at": "2013-10-02T09:24:18Z"
   }
diff --git a/lib/api/entities.rb b/lib/api/entities.rb
index 0246f36a685..65f615b7d28 100644
--- a/lib/api/entities.rb
+++ b/lib/api/entities.rb
@@ -501,6 +501,9 @@ module API
       expose :state, :created_at, :updated_at
       expose :due_date
       expose :start_date
+      expose :percentage_complete do |milestone, options|
+        milestone.percent_complete(options[:current_user])
+      end
 
       expose :web_url do |milestone, _options|
         Gitlab::UrlBuilder.build(milestone)
diff --git a/lib/api/milestone_responses.rb b/lib/api/milestone_responses.rb
index a0ca39b69d4..4c68c568aaa 100644
--- a/lib/api/milestone_responses.rb
+++ b/lib/api/milestone_responses.rb
@@ -35,19 +35,19 @@ module API
           milestones = filter_by_iid(milestones, params[:iids]) if params[:iids].present?
           milestones = filter_by_search(milestones, params[:search]) if params[:search]
 
-          present paginate(milestones), with: Entities::Milestone
+          present paginate(milestones), with: Entities::Milestone, current_user: current_user
         end
 
         def get_milestone_for(parent)
           milestone = parent.milestones.find(params[:milestone_id])
-          present milestone, with: Entities::Milestone
+          present milestone, with: Entities::Milestone, current_user: current_user
         end
 
         def create_milestone_for(parent)
           milestone = ::Milestones::CreateService.new(parent, current_user, declared_params).execute
 
           if milestone.valid?
-            present milestone, with: Entities::Milestone
+            present milestone, with: Entities::Milestone, current_user: current_user
           else
             render_api_error!("Failed to create milestone #{milestone.errors.messages}", 400)
           end
@@ -60,7 +60,7 @@ module API
           milestone = ::Milestones::UpdateService.new(parent, current_user, milestone_params).execute(milestone)
 
           if milestone.valid?
-            present milestone, with: Entities::Milestone
+            present milestone, with: Entities::Milestone, current_user: current_user
           else
             render_api_error!("Failed to update milestone #{milestone.errors.messages}", 400)
           end
diff --git a/spec/fixtures/api/schemas/public_api/v4/milestone.json b/spec/fixtures/api/schemas/public_api/v4/milestone.json
index 6ca2e88ae91..971f7980f46 100644
--- a/spec/fixtures/api/schemas/public_api/v4/milestone.json
+++ b/spec/fixtures/api/schemas/public_api/v4/milestone.json
@@ -8,6 +8,7 @@
     "title": { "type": "string" },
     "description": { "type": ["string", "null"] },
     "state": { "type": "string" },
+    "percentage_complete": { "type": "integer" },
     "created_at": { "type": "date" },
     "updated_at": { "type": "date" },
     "start_date": { "type": "date" },
diff --git a/spec/support/api/milestones_shared_examples.rb b/spec/support/api/milestones_shared_examples.rb
index 5f709831ce1..b426fadb001 100644
--- a/spec/support/api/milestones_shared_examples.rb
+++ b/spec/support/api/milestones_shared_examples.rb
@@ -8,12 +8,17 @@ shared_examples_for 'group and project milestones' do |route_definition|
 
   describe "GET #{route_definition}" do
     it 'returns milestones list' do
+      create(:issue, project: project, milestone: milestone)
+      create(:closed_issue, project: project, milestone: milestone)
+      create(:closed_issue, project: project, milestone: milestone)
+
       get api(route, user)
 
       expect(response).to have_gitlab_http_status(200)
       expect(response).to include_pagination_headers
       expect(json_response).to be_an Array
       expect(json_response.first['title']).to eq(milestone.title)
+      expect(json_response.first['percentage_complete']).to eq(66)
     end
 
     it 'returns a 401 error if user not authenticated' do