Four modes, because “percentage” is four different questions
People search one phrase and mean four jobs. What is 18% of this invoice. This score is what percent of the total. The SIP jumped from 100 to 125 — is that 25% or 20%. Apply a 12% hike to last year’s CTC line. I put all four on one live strip so you stop opening four tabs and arguing about which algebra the other person used. There is no Calculate button. Type. The strip moves.
The algebra is grade-school and still the cause of quiet invoice fights. JavaScript floats will give you a long tail; for rupees, round the way your ledger already rounds (usually two decimals, sometimes none). This page is a napkin, not Tally.
Worked example: 18% of ₹1,180 (percent of)
Mode “What is X% of Y.” First number 18, second 1180. Result 212.4. That is an 18% line on an exclusive amount of ₹1,180 — the shape of a GST-exclusive invoice before you argue about rounding. Same mode, 18 and 1000 → 180. If your vendor quoted ₹1,180 inclusive, do not use this mode to “extract” GST; the GST calculator is the inclusive/exclusive tool. This one only multiplies.
Worked example: reverse percent — 45 is what percent of 60
Mode “X is what % of Y.” 45 and 60 → 75%. That is marks, win rate, occupancy, or “how much of the target did we actually hit.” Reverse GST sits here too: ₹180 tax on a ₹1,000 base is 18% — paste 180 and 1000. If the whole is 0, the page refuses, because dividing by zero is not a business insight. People mix this mode with percent-of and then swear the GST rate “changed.” It did not. You asked a different question.
Worked example: 100 → 125 is +25%; 125 → 100 is −20%
Mode “% change from A to B.” From 100 to 125: (125 − 100) / 100 = 25%. From 125 to 100: (100 − 125) / 125 = −20%. Same ₹25 gap, different denominator. This is the argument that shows up every quarter in a mutual-fund WhatsApp group and every time a product manager says “we only dropped 20% from the peak.” Peak-to-trough and trough-to-peak are not mirrors. I default the placeholders to 100 and 125 so you see it once with your own eyes. Starting value 0 is refused; you cannot percent-change from nothing.
Worked example: apply 12% to ₹85,000 (hike) and −20% to ₹2,499 (discount)
Mode “Apply % to amount.” Amount 85000, percent 12 → 95200. That is last year’s number with a 12% increment, the sketch people do before HR publishes the letter. Amount 2499, percent −20 → 1999.2, a catalogue discount. Positive percent increases; negative decreases. This is not compound interest and not a second discount stacked on the first. Ten percent off, then another ten, is 0.9 × 0.9 = 19% off, not 20. Run apply twice if a retailer stacked them. Once if they did not.
What I will not pretend this is
CAGR, SIP step-up, EMI, or “increase of 10% per year for 8 years.” Those are other pages. Successive markups that finance teams call “plus plus.” Exam boards that count words differently than percentages. Tip-plus-GST-plus-service-charge stacks that restaurants invent at 11pm — compute each line, do not hope one percentage ate the others. If the number matters on a filing, use the software that already holds the invoice, not this strip.
What are the four modes?
What is X% of Y; X is what percent of Y (reverse); percent change from A to B; apply a percent increase or decrease to an amount.
Why is 100→125 not the reverse of 125→100?
Percent change divides by the starting number. 100 to 125 is +25%. 125 to 100 is −20%. The rupee gap is the same; the percentages are not.
Can I reverse a GST line here?
If ₹180 is 18% of a base, use “X is what % of Y” with 180 and 1000, or “what is X% of Y” the other way. Inclusive GST stacks belong on the GST calculator.
Does this do successive discounts?
No. 10% off then 10% off is not 20% off. Chain the apply mode twice if you must; retail sites hope you will not.
Tip, markup, or exam scores?
All of those are “percent of” or “part of whole.” Round the way your invoice or marksheet rounds — this display is not a ledger.
Are the numbers uploaded?
No. Two numbers stay in this tab. Watch the compute log.