What is 30% of 40? 12 30% of 40 Copy 30% of 40 = 12. Formula UsedResult = (30 ÷ 100) × 40 = 12 Frequently Asked Questions What is 30% of 40?12. (30 ÷ 100) × 40 = 12.How to calculate 30%?Multiply by 0.3 (or multiply by 30 then divide by 100).