Comprehensive Calculator Guide
To increase a number by a percentage, multiply it by (1 + rate ÷ 100). A salary of SAR 8,000 rising 10% becomes 8,000 × 1.10 = SAR 8,800, an increase of SAR 800. The calculator also works backwards: enter the new value and the rate to get the original, or both values to get the rate.
How a percentage increase works
A percentage is a part per hundred, so the increase is value × rate ÷ 100 and the new value is the two added. Faster still, multiply by the growth factor: 1.10 for 10%, 1.15 for 15%. A SAR 200 item with 15% VAT costs 200 × 1.15 = SAR 230.
To undo an increase, divide by the factor rather than subtracting the rate: SAR 1,000 after a 25% rise was 1,000 ÷ 1.25 = SAR 800, not 750.
Successive increases compound
Two 10% rises are 21%, not 20%, because the second applies to the already raised amount: 1.10 × 1.10 = 1.21. Multiply the factors for any chain of increases.
How to Use
- 01Enter the original value and the rate to get the new value and the amount added.
- 02To find the original, enter the new value and the rate and leave the original empty.
- 03To find the rate, enter the original and the new value.
Formula Used
New value = value × (1 + rate ÷ 100) | Original = new value ÷ (1 + rate ÷ 100)Practical Examples
Example 1: a pay rise
SAR 8,000 plus 10%: SAR 8,800, an increase of SAR 800.
Example 2: adding VAT
SAR 200 plus 15%: SAR 230.
Example 3: before the increase
SAR 1,000 after a 25% rise: originally SAR 800.
Important Tips
- Turn a rate into a factor by dividing by 100 and adding 1: 7% is 1.07.
- For a chain of increases, multiply the factors.
Common Mistakes to Avoid
- Subtracting the rate from the new value to find the original.
- Adding successive rates instead of multiplying factors.
Frequently Asked Questions
- How do I add 15% to an amount?
- Multiply by 1.15: SAR 2,000 becomes SAR 2,300.
- How do I find the increase between two numbers?
- Divide the difference by the old value and multiply by 100: 8,000 to 9,200 is 15%.
- How do I find the amount before an increase?
- Divide by (1 + rate ÷ 100): 1,150 after 15% was 1,000.
- Are two 10% rises the same as 20%?
- No, they make 21%.