estimate, underestimate and overestimate

estimate

/ˈestɪmeɪt/  verb transtive         "to value, esteem," 

​to form an idea of the cost, size, value etc. of something, but without calculating it exactly

• to estimate the cost/value/number of something
• I estimated that three days would be enough for the user story.

estimate
 /ˈestɪmət/ noun countable, uncountable
​  a judgement that you make without having the exact details or figures about the size, amount, cost, etc. of something

• to provide/obtain an estimate
• My estimate is three weeks.

underestimate verb
 /ˌʌndərˈestɪmeɪt/ transitive
​to think or guess that the amount, cost or size of something is smaller than it really is

•  to underestimate the cost of the project
• My supervisor told me I underestimated how long the user story would take.

underestimate noun
 /ˌʌndərˈestɪmət/
(also underestimation  /ˌʌndərˌestɪˈmeɪʃn/ [countable, uncountable])
​an estimate about the size, cost, etc. of something that is too low

• My guess of 400 proved to be a serious underestimate.
• I admitted that 3 days was a serious underestimate.

overestimate

verb

I didn't overestimate the time the user story would cost.

overestimate

noun (also overestimation)

I pretended three weeks was an overestimate.