What is 40% of 30?
The answer is 12.
Result Explanation
40% of 30 = 12. If you are subtracting this as a discount, the discounted total is 30 − 12 = 18. If you are allocating, 12 is the allocated amount and 18 is the remainder.
Quick check: compare 30 × 0.4 with (40 ÷ 100) × 30; both should equal 12.
How It Works
Step 1: Express 40% as a decimal: 40 ÷ 100 = 0.4.
Step 2: Multiply by 30: 0.4 × 30 = 12.
Full formula: (40 ÷ 100) × 30 = 12
Fraction shortcut: 40% = 2/5; (2/5) × 30 = 12.
Ten-percent ladder: 10% of 30 is 3; 40% = 4 × 3 = 12.
Strategy & Insight
Compare with fifteen: forty percent of fifteen is 6, and doubling the base to thirty doubles the slice to 12 while the rate holds. That proportional check catches a missing zero or a mis-scoped subtotal faster than re-deriving from scratch.
At forty percent, each one-unit move in the base changes the absolute amount by 0.4. From twenty-nine to thirty-one, the slice moves by eight tenths around your answer—tiny on paper, but the same linear sensitivity you see on invoices in the thousands.
Common Mistakes
- Multiplying 30 by 40 instead of 0.4.
- Quoting 18 when the prompt asked only for the forty percent share.
- Confusing forty percent of thirty with adding forty percent to thirty.
- Using a 31-day month mentally but labelling the base as 30 without adjusting.
Pro Tip
Lock in 10% of 30 = 3. Four steps of that size give forty percent: 12. On sixty, each ten-percent step is six, so forty percent is twenty-four—same rate, wider stride.
Examples
Example 1: Class or cohort
Out of 30 learners, forty percent pass a gate on the first attempt in a simple model: 12 people sit in that band and 18 sit outside it before resits or appeals.
Example 2: Thirty-pound basket
A £30.00 basket assigns forty percent of the subtotal to a tagged category: £12.00 on that tag and £18.00 elsewhere before delivery or VAT rules apply.
Example 3: Thirty-day horizon
On a planning strip of 30 working days, forty percent reserved for deep work is 12 days, with 18 days left for meetings and maintenance in the naive split.
Related Links
FAQ
What is 40% of 30?
40% of 30 is 12.
How do you calculate 40% of 30?
Multiply 30 by 0.4, take two fifths of 30, or stack four lots of 10% (3) to reach 12.
What is 30 minus 40%?
Removing the 40% portion (12) from 30 leaves 18.
How does 40% of 30 relate to 40% of 15?
Doubling the base from 15 to 30 doubles the forty percent slice from 6 to 12 while the rate stays the same.