Sarah from TurboTax discusses important information on getting your penalties waived.

Not paying your taxes on time can result not only in interest, but penalties which can tack on up to another 25% onto what you already owe.

However, the IRS is permitted to reduce, or otherwise eliminate penalties if you qualify. To qualify, you will need to show that certain underlying circumstances existed, or currently exist, that should be taken into consideration.  For example, the loss of tax documents in a disaster, a serious illness or the death of a family member would often qualify for relief of penalties you may owe.

Just saying that such factors existed is usually not enough. In these cases, you will be asked to support, or provide evidence that such factors existed.

Missing deadlines due to ignorance will almost always not suffice.