County Auditor Bulletins
Ohio law requires the General Assembly to pass legislation, when federal law is changed, in order to adopt, or conform to, those changes for Ohio tax purposes. As of March 30, 2018, Ohio is in conformity for tax years 2017 and prior. For the most recent conformity announcement, see the following link:
Applies to taxable year 2017 (PDF)
Ohio's conformity statute is found in O.R.C. 5701.11. Division (A) of O.R.C. 5701.11 states that any reference in the tax chapters of the Revised Code to the "Internal Revenue Code" means the Internal Revenue Code as it exists on the effective date of the statute (currently March 30, 2018).
Division (B)(1) of the O.R.C. 5701.11 allows a taxpayer to irrevocably elect either 1) the version of the Internal Revenue Code that existed at the end of the taxpayer's taxable year or 2) the version of the Internal Revenue Code as it existed after Ohio conformity under O.R.C. 5701.11(A). This election exists to allow taxpayers to take advantage of relevant tax deductions/ credits that become part of Ohio law after the close of the taxpayer's tax year, while also avoiding retroactive tax increases.
Please note: A taxpayer must elect one version of the Internal Revenue Code or the other; the taxpayer cannot selectively incorporate some provisions from each version of the IRC.