The Ohio marital deduction is a deduction allowed a surviving spouse, equal to the net value of assets passing from the decedent. For example: If the decedent left an estate valued at $400,000 and all assets passed to the surviving spouse, the spouse would be allowed a deduction of $400,000, reducing the Ohio estate tax to zero. Even though the marital deduction may reduce the Ohio estate tax to zero, a return must still be filed.