The word guesstimate is an amalgamation of the words 'guess' and 'estimate'. A guesstimate is an educated guess or an informed estimate made by someone who has a good idea of something but has not had time to come up with a correct answer or to calculate something fully.

1. I believe that the company's turnover will increase by around 10% this year. Don't take that to be a fact though, I'm just making a guesstimation.
2. I'm aware that most of the facts and figures aren't in yet, but could you at least give me a guesstimate of what our sales numbers are?

1. If I had to guesstimate, I would say ten homes on this street were sold last year.
2. I'm not sure what age he is, but I know he is retired, so If I had to make a guesstimate I'd say he might be around 67.