You may carry over only that portion of the credit that you do not apply to tax. You cannot carry over any amount that you paid that was more than the amount allowed as a credit.If the allowable tax credit is more than your tax or if you have no tax, you may carry the unused credit forward for up to the next five consecutive taxable years’ income tax liability. 

For example: last year, John, a single person, paid $400 to School A for extra curricular activity fees for John's child. Last year, John is allowed a credit of $200. His tax due was $100. John may carryover $100 of the unused $200 credit to this year. John cannot claim any credit for the $200 fee he paid that was more than the allowable credit ($400 minus allowable credit of $200).