Navigating the complex landscape of program cost estimation requires confronting hidden biases that threaten budgets, timelines, and ultimately mission success. Accurate cost estimating is critical for defense programs aiming to deliver on time, within budget, and with the capabilities needed for today’s warfighter. Yet, cost estimation—especially early in the acquisition process—is often undermined by inherent biases that lead to budget overruns and delayed fielding. Understanding these biases and proactively addressing them significantly improves the accuracy and reliability of cost forecasts.