diff --git a/modules/bidViewability.js b/modules/bidViewability.js
index a5cab99b1a7..be18095e369 100644
--- a/modules/bidViewability.js
+++ b/modules/bidViewability.js
@@ -67,6 +67,8 @@ export let logWinningBidNotFound = (slot) => {
 
 export let impressionViewableHandler = (globalModuleConfig, slot, event) => {
   let respectiveBid = getMatchingWinningBidForGPTSlot(globalModuleConfig, slot);
+  let respectiveDeferredAdUnit = getGlobal().adUnits.find(adUnit => adUnit.deferBilling && respectiveBid.adUnitCode === adUnit.code);
+
   if (respectiveBid === null) {
     logWinningBidNotFound(slot);
   } else {
@@ -74,6 +76,11 @@ export let impressionViewableHandler = (globalModuleConfig, slot, event) => {
     fireViewabilityPixels(globalModuleConfig, respectiveBid);
     // trigger respective bidder's onBidViewable handler
     adapterManager.callBidViewableBidder(respectiveBid.adapterCode || respectiveBid.bidder, respectiveBid);
+
+    if (respectiveDeferredAdUnit) {
+      adapterManager.callBidBillableBidder(respectiveBid);
+    }
+
     // emit the BID_VIEWABLE event with bid details, this event can be consumed by bidders and analytics pixels
     events.emit(CONSTANTS.EVENTS.BID_VIEWABLE, respectiveBid);
   }
diff --git a/modules/bidViewability.md b/modules/bidViewability.md
index 78a1539fb1a..922a4a9def4 100644
--- a/modules/bidViewability.md
+++ b/modules/bidViewability.md
@@ -2,19 +2,20 @@
 
 Module Name: bidViewability
 
-Purpose: Track when a bid is viewable
+Purpose: Track when a bid is viewable (and also ready for billing)
 
 Maintainer: harshad.mane@pubmatic.com
 
 # Description
-- This module, when included, will trigger a BID_VIEWABLE event which can be consumed by Analytics adapters, bidders will need to implement `onBidViewable` method to capture this event
-- Bidderes can check if this module is part of the final build and whether it is enabled or not by accessing ```pbjs.getConfig('bidViewability')```
+- This module, when included, will trigger a BID_VIEWABLE event which can be consumed by Analytics adapters, bidders will need to implement the `onBidViewable` method to capture this event
+- Bidders can check if this module is part of the final build and whether it is enabled or not by accessing ```pbjs.getConfig('bidViewability')```
 - GPT API is used to find when a bid is viewable, https://developers.google.com/publisher-tag/reference#googletag.events.impressionviewableevent . This event is fired when an impression becomes viewable, according to the Active View criteria.
 Refer: https://support.google.com/admanager/answer/4524488
-- The module does not work with adserver other than GAM with GPT integration
+- This module does not work with any adserver's other than GAM with GPT integration
 - Logic used to find a matching pbjs-bid for a GPT slot is ``` (slot.getAdUnitPath() === bid.adUnitCode || slot.getSlotElementId() === bid.adUnitCode) ``` this logic can be changed by using param ```customMatchFunction```
-- When a rendered PBJS bid is viewable the module will trigger BID_VIEWABLE event, which can be consumed by bidders and analytics adapters
-- For the viewable bid if ```bid.vurls type array``` param is and module config ``` firePixels: true ``` is set then the URLs mentioned in bid.vurls will be executed. Please note that GDPR and USP related parameters will be added to the given URLs
+- When a rendered PBJS bid is viewable the module will trigger a BID_VIEWABLE event, which can be consumed by bidders and analytics adapters
+- If the viewable bid contains a ```vurls``` param containing URL's and the Bid Viewability module is configured with ``` firePixels: true ``` then the URLs mentioned in bid.vurls will be called. Please note that GDPR and USP related parameters will be added to the given URLs
+- This module is also compatible with Prebid core's billing deferral logic, this means that bids linked to an ad unit marked with `deferBilling: true` will trigger a bid adapter's `onBidBillable` function (if present) indicating an ad slot was viewed and also billing ready (if it were deferred).
 
 # Params
 - enabled [required] [type: boolean, default: false], when set to true, the module will emit BID_VIEWABLE when applicable
@@ -44,6 +45,6 @@ Refer: https://support.google.com/admanager/answer/4524488
 ```
 
 # Please Note:
-- Doesn't seems to work with Instream Video, https://docs.prebid.org/dev-docs/examples/instream-banner-mix.html as GPT's impressionViewable event is not triggered for instream-video-creative
-- Works with Banner, Outsteam, Native creatives
+- This module doesn't seem to work with Instream Video, https://docs.prebid.org/dev-docs/examples/instream-banner-mix.html as GPT's impressionViewable event is not triggered for instream-video-creative
+- Works with Banner, Outsteam and Native creatives
 
diff --git a/test/spec/modules/bidViewability_spec.js b/test/spec/modules/bidViewability_spec.js
index a822d86f852..2d2e51abbe1 100644
--- a/test/spec/modules/bidViewability_spec.js
+++ b/test/spec/modules/bidViewability_spec.js
@@ -245,18 +245,31 @@ describe('#bidViewability', function() {
     let logWinningBidNotFoundSpy;
     let callBidViewableBidderSpy;
     let winningBidsArray;
+    let callBidBillableBidderSpy;
+    let adUnits = [
+      {
+        'code': 'abc123',
+        'bids': [
+          {
+            'bidder': 'pubmatic'
+          }
+        ]
+      }
+    ];
 
     beforeEach(function() {
       sandbox = sinon.sandbox.create();
       triggerPixelSpy = sandbox.spy(utils, ['triggerPixel']);
       eventsEmitSpy = sandbox.spy(events, ['emit']);
       callBidViewableBidderSpy = sandbox.spy(adapterManager, ['callBidViewableBidder']);
+      callBidBillableBidderSpy = sandbox.spy(adapterManager, ['callBidBillableBidder']);
       // mocking winningBidsArray
       winningBidsArray = [];
       sandbox.stub(prebidGlobal, 'getGlobal').returns({
         getAllWinningBids: function (number) {
           return winningBidsArray;
-        }
+        },
+        adUnits
       });
     });
 
@@ -293,5 +306,23 @@ describe('#bidViewability', function() {
       // CONSTANTS.EVENTS.BID_VIEWABLE is NOT triggered
       expect(eventsEmitSpy.callCount).to.equal(0);
     });
+
+    it('should call the callBidBillableBidder function if the viewable bid is associated with an ad unit with deferBilling set to true', function() {
+      let moduleConfig = {};
+      const deferredBillingAdUnit = {
+        'code': '/harshad/Jan/2021/',
+        'deferBilling': true,
+        'bids': [
+          {
+            'bidder': 'pubmatic'
+          }
+        ]
+      };
+      adUnits.push(deferredBillingAdUnit);
+      winningBidsArray.push(PBJS_WINNING_BID);
+      bidViewability.impressionViewableHandler(moduleConfig, GPT_SLOT, null);
+      expect(callBidBillableBidderSpy.callCount).to.equal(1);
+      sinon.assert.calledWith(callBidBillableBidderSpy, PBJS_WINNING_BID);
+    });
   });
 });