diff --git a/README.md b/README.md
index ed578a2..a9780f0 100644
--- a/README.md
+++ b/README.md
@@ -48,6 +48,17 @@ You can also define a function, that'll receive current progress and for example
 </AnimatedCircularProgress>
 ```
 
+Finally, you can manually trigger a duration-based timing animation by putting a ref on the component and calling the `performLinearAnimation(toValue, duration)` function like so:
+```jsx
+<AnimatedCircularProgress
+  ref='circularProgress'
+  ...
+/>
+```
+```javascript
+this.refs.circularProgress.performLinearAnimation(100, 8000); // Will fill the progress bar linearly in 8 seconds
+```
+
 ## Configuration
 
 You can configure the passing by following props:
diff --git a/src/AnimatedCircularProgress.js b/src/AnimatedCircularProgress.js
index 8e6238c..0a7333f 100644
--- a/src/AnimatedCircularProgress.js
+++ b/src/AnimatedCircularProgress.js
@@ -33,6 +33,13 @@ export default class AnimatedCircularProgress extends React.Component {
       }
     ).start();
   }
+  
+  performLinearAnimation(toValue, duration) {
+    Animated.timing(this.state.chartFillAnimation, {
+      toValue: toValue,
+      duration: duration
+    }).start();
+  }
 
   render() {
     const { fill, prefill, ...other } = this.props;
@@ -49,7 +56,7 @@ export default class AnimatedCircularProgress extends React.Component {
 AnimatedCircularProgress.propTypes = {
   style: View.propTypes.style,
   size: PropTypes.number.isRequired,
-  fill: PropTypes.number.isRequired,
+  fill: PropTypes.number,
   prefill: PropTypes.number,
   width: PropTypes.number.isRequired,
   tintColor: PropTypes.string,