Calculate your tax liability. If you are over the age of 59-1/2, you will only need to pay income tax for the year that the funds were paid to you. If you are under the age of 59-1/2, you will be subject to an additional penalty of 10 percent, or 25 percent if you have participated in the plan for less than 2 years.
Determine how long you have participated in your Simple IRA. The "2-year period" rule will increase your withdrawal tax penalty from 10 percent to 25 percent if you are under 59-1/2 years of age and you have been contributing to the plan for less than 2 years. The 2-year period begins on the date that you first participated in the Simple IRA plan offered by your employer.
For more you can refer to this site.