You are running a project which was budgeted based on some rough order of magnitude (ROM) estimates with a precision of -25%/ +75%. Meanwhile, with new estimates made at the detail level and some work already finished, you found out that these estimates were consistently too low and the budget will not be sufficient to successfully run and finish the project. What should you do? Try to reduce scope or quality in areas where it cannot create difficulties for you and the team. Finally, it is not your responsibility that an insufficient budget has been created for the project. Find a contractor who can run the project for you. Set the budget as a price limit during the bidding process and accept only form fixed price (FFP) offers which do not exceed this price. Bring the issue to your sponsor and discuss how this should be handled. Together with the sponsor adhere to the guidelines which describe how budgets will be reviewed and refined. You shouldn't worry too much, it is quite normal that early estimates are too optimistic, later estimates are too pessimistic and the project costs will finally settle somewhere in between. So relax