Personally, I always give my estimates as a range. If you break down your project into small tasks, and estimate each task as an optimistic/pessimistic range, then you can get a pretty good idea of the expected completion date, along with the deviations from that which you might reasonably expect.
However good your estimate, committing to ONE number is madness - it hides the complexity of the situation, making it impossible for you or your manager to see the real picture.
Never, ever say this.
Personally, I always give my estimates as a range. If you break down your project into small tasks, and estimate each task as an optimistic/pessimistic range, then you can get a pretty good idea of the expected completion date, along with the deviations from that which you might reasonably expect.
However good your estimate, committing to ONE number is madness - it hides the complexity of the situation, making it impossible for you or your manager to see the real picture.