An educated guess
Definition 1 of 1
Pro Tip 1/3Knowledge-Based
Use 'an educated guess' when you draw conclusions from your knowledge or past experiences. 
I don't have the report, but based on sales trends, my educated guess is we've improved our market share.
Pro Tip 2/3Not Certain
'An educated guess' indicates you're not 100% certain, but you believe your assumption is close to reality. 
Without seeing the essay, I can make an educated guess that it discusses historical causes.
Pro Tip 3/3Formal Conversations
It's more appropriate in formal settings where stating assumptions with some basis is necessary. 
An educated guess suggests the merger will happen within the next fiscal year.