diff --git a/CHANGELOG.md b/CHANGELOG.md
index b13014e..be80cbe 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [1.3.X]
 
+
+- Update time spent calculation for EventSource block
 - Remove support for system event tracing (Updated the wiki to create wrapper for system event tracing)
 
 ## [1.2.X] - 2018.02.24
diff --git a/README.md b/README.md
index d80c060..6076469 100644
--- a/README.md
+++ b/README.md
@@ -453,7 +453,7 @@ end
 
 ## Traceability
 
-EventBus comes with a good enough data structure to track the event life cycle with its optional parameters. For a traceable system, it is highly recommend to fill optional fields on event data. It is also encouraged to use `Event.nofify` block/yield to automatically set the `initialized_at` and `occurred_at` values.
+EventBus comes with a good enough data structure to track the event life cycle with its optional parameters. For a traceable system, it is highly recommend to fill optional fields on event data. It is also encouraged to use `EventSource.nofify` block/yield to automatically set the `initialized_at` and `occurred_at` values.
 
 ### System Events
 
diff --git a/lib/event_bus/event_source.ex b/lib/event_bus/event_source.ex
index 89961f8..fd54f32 100644
--- a/lib/event_bus/event_source.ex
+++ b/lib/event_bus/event_source.ex
@@ -9,6 +9,7 @@ defmodule EventBus.EventSource do
   defmacro __using__(_) do
     quote do
       require EventBus.EventSource
+
       alias EventBus.EventSource
       alias EventBus.Model.Event
     end
@@ -20,6 +21,7 @@ defmodule EventBus.EventSource do
   """
   defmacro build(params, do: yield) do
     quote do
+      started_at = System.monotonic_time(:micro_seconds)
       initialized_at = System.os_time(:micro_seconds)
       params = unquote(params)
 
@@ -35,13 +37,15 @@ defmodule EventBus.EventSource do
             {params[:topic], result}
         end
 
+      time_spent = System.monotonic_time(:micro_seconds) - started_at
+
       %Event{
         id: params[:id],
         topic: topic,
         transaction_id: params[:transaction_id],
         data: data,
         initialized_at: initialized_at,
-        occurred_at: System.os_time(:micro_seconds),
+        occurred_at: initialized_at + time_spent,
         source: source,
         ttl: params[:ttl]
       }