From Page 29 of the NY Instructions for Form IT-203:
Line 45 – Income percentage:
To compute your income percentage, divide the amount from line 31 in the New York State amount column by the amount from line 31 in the Federal amount column. (These amounts must be entered in the boxes to the left of line 45.) Round the result to the fourth decimal place. For example, if the amounts used were $12,000 divided by $36,000, the result would be .3333. Enter this decimal on line 45; do not convert to a percentage.
https://www.tax.ny.gov/pdf/current_forms/it/it203i.pdf
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
