1. You didn't have enough withheld.
2. You had other income besides wages.
3. Ohio tax brackets are the same for Singles and for MFJ. So, for example, let's say you each make $30,000. Your individual tax bracket ($30,000) is 2.969%. But together ($60,000) it is 3.465%.
https://www.incometaxpro.net/tax-rates/ohio.htm
