Reverse percentage

Client

If a price grew 20% to $120, the original was $100—this inverts percent change without spreadsheet formulas.

How to use

Enter final amount, then percent and inc/dec (e.g. 20 inc).

About Reverse percentage

Given a final amount after a percent increase or decrease, find the original—local percent algebra. The interactive transform on this page runs in your browser tab—Toolcore does not need your paste for the core operation described above.

How to use this page

Paste or type in the main workspace, run the primary action from the toolbar, then copy or download the result. Use Load example when the page offers it, or URL prefill (?q= / ?qb=) so agents and tickets open the same input.

Original ≈ 100 (after 20% increase → 120)

Nearby workflows on Toolcore

  • Percent change — Calculate percentage increase or decrease from an old value to a new one—local math in your browser. when units or numeric output should be checked on a related calculator.
  • Percentage calculator — Percent of a value, ratio to percent, and percent change—no server round-trip. when units or numeric output should be checked on a related calculator.
  • Discount calculator — Original price and discount percent—savings and final price in your browser. when units or numeric output should be checked on a related calculator.
  • Markup percent calculator — Selling price and profit from cost and markup percentage. when units or numeric output should be checked on a related calculator.

Common use cases

  • Back out pre-tax or pre-markup amounts from a labeled final price.
  • Verify retail “was/now” sale math in shopping comparisons.

Common mistakes to avoid

  • Using the original as input

    Enter the final (after change) amount in the first field.

FAQ

Decrease syntax?

Use "15 dec" or "15 decrease" in the second field.

Sales tax?

Single-step percent only—compound steps need separate passes.

More tools

Related utilities you can open in another tab—mostly client-side.