What is 40% of 30? 12 40% of 30 Copy 40% of 30 = 12. Formula UsedResult = (40 ÷ 100) × 30 = 12 Frequently Asked Questions What is 40% of 30?12. (40 ÷ 100) × 30 = 12.How to calculate 40%?Multiply by 0.4 (or multiply by 40 then divide by 100).