Interactive Increase and Decrease Calculator
Use this tool to quickly increase a value, decrease a value, calculate percentage change, or reverse a previous percentage adjustment.
This finds the original value before the percentage change happened.
What Is an Increase and Decrease Calculator?
An increase and decrease calculator is a quick way to apply percentage changes to any number. Whether you are adjusting a product price, evaluating salary growth, planning a budget cut, or checking investment performance, percentage calculations help you compare values clearly.
This page gives you three useful tools in one:
- Increase or decrease a value by a chosen percentage.
- Find percentage change between an old value and a new value.
- Reverse a change to recover the original value.
How to Use the Calculator
1) Increase or Decrease a Value
Pick the first mode, enter your starting value and percentage, choose increase or decrease, then click calculate. You will get the final value and the exact amount changed.
2) Find Percentage Change
Choose the second mode, input old and new values, and calculate. The result tells you whether the value increased or decreased and by what percent.
3) Reverse an Increase or Decrease
Choose the reverse mode when you already know the final number and the percentage applied. This is useful when a discounted or marked-up number is known but the original value is missing.
Core Percentage Formulas
Increase Formula
New Value = Original Value × (1 + Percentage ÷ 100)
Decrease Formula
New Value = Original Value × (1 - Percentage ÷ 100)
Percentage Change Formula
Percentage Change = ((New - Old) ÷ Old) × 100
If the result is positive, it is an increase. If negative, it is a decrease.
Reverse Formula
If the final number came after an increase:
Original = Final ÷ (1 + Percentage ÷ 100)
If the final number came after a decrease:
Original = Final ÷ (1 - Percentage ÷ 100)
Practical Everyday Examples
Pricing and Discounts
A shirt priced at 80 with a 25% discount becomes 60. If all you know is the final 60 and the 25% discount, reverse mode gives you the original 80.
Salary Planning
If your salary rises from 52,000 to 55,120, percentage change helps you verify your raise rate before accepting projections or offers.
Budget and Cost Control
When a team budget is reduced by 12%, decrease mode instantly estimates the new spending limit, making planning faster and more accurate.
Common Mistakes to Avoid
- Using the wrong base value: Percent change should usually be based on the old/original value.
- Confusing percentage points with percent: A move from 10% to 15% is a 5 percentage-point increase, but a 50% relative increase.
- Forgetting reverse math: A 20% increase followed by a 20% decrease does not return to the original value.
- Ignoring signs: Positive results represent growth; negative results represent decline.
Frequently Asked Questions
Can I use decimals?
Yes. The calculator supports decimal values and decimal percentages.
What happens if the old value is zero in percentage change mode?
Percentage change cannot be computed from zero because division by zero is undefined. In that case, use an absolute difference instead of a percentage.
Can percentages be greater than 100?
Yes. More than 100% increase is valid. For decreases, 100% means the value drops to zero, and anything above 100% can produce a negative result.
Final Thoughts
If you deal with money, growth metrics, performance reports, or forecasts, quick percentage tools save time and reduce mistakes. Use the calculator above whenever you need reliable increase, decrease, or percent-change math in seconds.