Answer rate is the percentage of your branded calls that were answered, while contact rate is the percentage of unique called numbers where they answered at least one time.
For example, if you called person A one time and they answered but person B didn’t answer the first time so you had to call them a second time before they picked up, your answer rate would be 66.7% (2/3 calls answered) but your contact rate would be 100% (2/2 people answered).
If you called person A one time and they answered, and you called person B four times and they never answered, your answer rate would be 20% (1/5 calls answered) and your contact rate would be 50% (1/2 people answered).
For more information, check out the INFORM Reporting Metrics & Definitions FAQ.