There is an older Splunk query here that had previously predicted license usage. I’m not sure why (perhaps the predict command has changed since the original post in 2015?), but the query is no longer working. I’ve updated the query to predict Splunk license usage using the Splunk predict command as shown below:

index=_internal source="*license_usage.lo*" type=Usage 
| eval GB=round(b/1024/1024/1024, 2) 
| timechart span=1d avg(GB) as Gigabytes 
| predict Gigabytes