Guesstimate (verb)

1. To make a rough estimate or approximation of a value or quantity.
2. To estimate, approximate, or predict something based on little or incomplete information.

Origin:

Combination of "guess" and "estimate" to describe a rough approximation of a value or quantity, a rough estimate.

Examples:

1. I guesstimated that the project would take about a month to complete.
2. I guesstimated that we would need about 50 attendees to make the event successful.
3. The market researcher guesstimated the size of the target market.
4. The contractor guesstimated the cost of the repairs.
5. The analyst guesstimated the company's future earnings based on the current data.