overestimate
n. B2 Upper Intermediate US //ˌoʊvɝˈɛstəˌmeɪt// UK //ˌəʊvəɹˈɛstɪmət// over·es·ti·mate
n. a guess or calculation that is higher than the actual amount or value. You use this when you think something is bigger, more expensive, or more important than it really is.
n. an estimate or calculation that is higher than the actual value or amount. Often used to describe a judgment that is too optimistic or exaggerated.
The initial overestimate of the project cost was quite high.
The team realized their overestimate of the available resources meant they had to delay the final phase of the construction.
While the initial overestimate of the market potential was criticized by analysts, it actually served as a catalyst for the company to develop more robust and scalable infrastructure.
From over- + estimate.