Software Estimation: Demystifying the Black Art (Best Practices (Microsoft))

Don't intentionally underestimate. The penalty for underestimation is more severe than the penalty for overestimation. Address concerns about overestimation through planning and control, not by biasing your estimates.

Recognize a mismatch between a project's business target and a project's estimate for what it is: valuable risk information that the project might not be successful. Take corrective action early, when it can do some good.

Many businesses value predictability more than development time, cost, or flexibility. Be sure you understand what your business values the most.