How I calculate percentages without doing mental math

Percentages are simple until the question changes: percentage of, percentage increase, percentage decrease, and reverse percentage are different tasks.

The Percentage Calculator tool handles the repetitive part so I can focus on checking whether the result makes sense.

The simple idea

Percentages are simple until the question changes: percentage of, percentage increase, percentage decrease, and reverse percentage are different tasks.

I still treat the output as something to review, especially when it affects money, dates, privacy, or production data.

Step 1: Choose the percentage question you are answering

Choose the percentage question you are answering.

Step 2: Enter the base number

Enter the base number.

Step 3: Enter the percentage value

Enter the percentage value.

Step 4: Check whether you need increase or decrease

Check whether you need increase or decrease.

Step 5: Read the final value and the difference

Read the final value and the difference.

Step 6: For money, check rounding rules

For money, check rounding rules.

Step 7: Do not mix percentage points with percent change

Do not mix percentage points with percent change.

My checklist

Before I trust the result, I check:

• Choose the percentage question you are answering.
• Enter the base number.
• Enter the percentage value.
• Check whether you need increase or decrease.
• Read the final value and the difference.
• For money, check rounding rules.
• Do not mix percentage points with percent change.

A small tool is most useful when it makes the work visible and easy to verify.