What is the Percentage Difference from 81 to 66?

Step by step

1. Difference: 66 − 81 = -15
2. Divide by the starting value: -15 ÷ 81 = -0.185185
3. Multiply by 100: -18.5185%

How the answer is worked out

Percentage change measures a difference against the value you started with. The value went from 81 to 66, a difference of 15. Compared with the starting value of 81, that difference is 18.5185%, so this is a 18.5185% decrease.

The new value is 81.4815% of the old one: for every 100 at the start there are now 81.4815, so 18.5185 out of every 100 have gone.

Why calculate this?

Percentage change compares a new value with an old one regardless of size: price rises, growth, discounts, score changes.

• Sales: a price cut from $81 to $66 is a 18.5185% discount.
• Weight: going from 81 to 66 kilograms is a loss of 18.5185% of the starting weight.
• Results: if a team scores 66 points this season after 81 last season, its total has dropped by 18.5185%.

A quicker way

Find 1% of the starting value: 81 ÷ 100 = 0.81. The difference of 15 is 18.5185 of those steps.

Percentage change is not the same as percentage points. If a rate moves from 81% to 66%, it changes by 15 percentage points, but by 18.5185% relative to where it started.

Check the answer

Work forwards from the start: 81 × (1 − 0.185185) = 81 × 0.814815 = 66. Getting 66 shows the answer is right.

Rounding

Rounded to a whole number the change is -19, to one decimal place -18.5 and to two decimal places -18.52. Round only at the end: rounding halfway through a calculation can change the last digit.

The formula explained

percentage change = (new value − old value) ÷ old value × 100. A positive result is an increase and a negative result is a decrease. The old value is always the base, which is why the change from A to B and from B to A are different percentages.

Another worked example: 16 to 9

1. Difference: 9 − 16 = -7
2. Divide by the starting value: -7 ÷ 16 = -0.4375
3. Multiply by 100: -43.75%

Other ways to ask this

The same calculation is often asked in other words. All of these have the answer above:

• Percentage decrease from 81 to 66
• What percent less is 66 than 81?
• 81 to 66 as a percent change
• How much did 81 fall going to 66, in percent?
• Relative change between 81 and 66

Terms used on this page

• Old value: the starting amount, used as the base of the percentage.
• New value: the amount after the change.
• Increase: a positive change: the new value is bigger.
• Percentage point: the plain difference between two rates, not a relative change.

The answer in other forms

Related results

The other way round: Percentage difference from 66 to 81

Doing it in a spreadsheet

In Excel, Google Sheets or Numbers type =(66-81)/81*100 into any cell. Replace the numbers with cell references (for example A1 and B1) to reuse the formula for a whole column.

Common mistakes

Always divide by the starting value, not the new one. A rise from 40 to 50 is +25%, but the fall from 50 back to 40 is −20%.

Practice examples

How this answer was calculated

The result is worked out from the numbers in this page's address when the page is opened, using exact arithmetic wherever possible and rounding only for display. Nothing is copied from a printed table. If you think an answer is wrong, please tell us through the contact page and we will check it.

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