Percentage Calculator

Two boxes, three answers, and which one you actually wanted

Most percentage calculators make you choose a mode first: “percentage of”, “is what percent”, “percent change”. People do not arrive knowing the name of the operation. They arrive with two numbers. So this page takes the two numbers and answers all three questions, and you read the line that matches your situation.

A% of B            = A / 100 x B
A is what % of B   = A / B x 100
Change from A to B = (B minus A) / |A| x 100

With the defaults, A = 40 and B = 52:

Line	Working	Result
Change from A to B	12 / 40 x 100	30.00%
A% of B	0.40 x 52	20.80
A is what % of B	40 / 52 x 100	76.92%
Difference (B minus A)	52 minus 40	12.00

Four numbers from the same pair, and they mean completely different things. If your salary went from ₹40,000 to ₹52,000, the line you want is the 30 percent change. If 40 of the 52 seats on the office bus are taken, it is 76.92 percent occupancy. If a shop is giving 40 percent off something priced ₹52, it is ₹20.80 off. Picking the wrong line is the most common percentage mistake there is, and it is why the labels say what each line is rather than just printing three numbers.

Marks out of 500, a salary hike, a Flipkart price drop and 18 percent GST

The same two boxes handle the four percentage questions people in India ask most, and each one uses a different line.

Board marks. 412 out of 500: put 412 in A, 500 in B, read “A is what % of B”: 82.40%. It works for 600 (most state boards), 720 (NEET) or the 30-mark internal your college gave you. If you are converting a CGPA rather than raw marks, the CGPA calculator uses the CBSE, VTU and standard rules instead of a plain division, because those are not plain divisions.

Appraisal season. Old CTC ₹40,000 a month in A, new CTC ₹52,000 in B, read the change: 30.00%. Two warnings from having watched this in April. Compare CTC with CTC, or in-hand with in-hand, never one with the other. And a hike that comes partly as variable pay is not a 30 percent hike in the month it does not pay out; the take-home salary calculator shows what actually lands.

A sale price. A t-shirt listed at ₹2,999 and now showing ₹1,999. MRP in A, sale price in B, read the change: minus 33.34%. The listing will say “33% off”, and that is the same number. Read “A is what % of B” and you get 150.03 percent, which is the wrong line: it says the MRP is 150 percent of the sale price, which is true and useless. For stacked offers, a bank-card discount on top of the tag discount, the discount calculator handles the order of operations.

GST on a quote. An 18 percent rate on a ₹2,500 job: 18 in A, 2500 in B, read “A% of B”: ₹450.00. The bill is ₹2,950. If you need the CGST and SGST split for an invoice, the GST calculator does that and handles inter-state IGST.

Percentage points and percent, with the RBI repo rate as the example

When the RBI cuts the repo rate from 6.50 to 6.25, every headline calls it a “25 basis point cut”. Put 6.5 in A and 6.25 in B and the calculator shows a difference of minus 0.25 and a change of minus 3.85%.

Both are right. The 0.25 is percentage points (a basis point is a hundredth of one), and it is the number that moves your floating-rate home loan, because the bank passes on the same 0.25 to its repo-linked lending rate. The 3.85 percent is how much smaller the rate itself is, and nobody prices a loan on it.

The confusion runs the other way with returns. A fund that went from a 10 percent annual return to 12 percent improved by 2 percentage points and by 20 percent, and the fund house’s advertisement will use whichever reads better. If a number in a headline seems too large for what happened, it is usually a percent-of-a-percent standing in for percentage points.

A related trap, and the one that costs money: a 50 percent fall is not undone by a 50 percent rise. ₹100 falling to ₹50 and rising 50 percent lands at ₹75. Getting back to ₹100 takes a 100 percent gain from the low. Each percentage is taken on whatever the current base is, and after a fall that base is smaller. For a stock or a mutual fund that dropped 30 percent, the recovery needed is 42.86 percent, not 30, and the ROI calculator will show what that means over a holding period.

Going backwards from a GST-inclusive bill or a post-hike salary

Reversing a percentage is where most hand arithmetic goes wrong, and the rule is short: divide, do not subtract.

A restaurant bill of ₹2,950 that includes 18 percent GST. The instinct is to take 18 percent off ₹2,950, which gives ₹2,419. The correct base is ₹2,950 divided by 1.18, which is ₹2,500, and the GST was ₹450. The subtraction is wrong by ₹81 because the 18 percent was charged on the smaller base, not on the total.

The same applies to a salary you only know after the hike. New CTC ₹52,000 after a 30 percent increase: the old figure was ₹52,000 divided by 1.30, which is ₹40,000. Taking 30 percent off ₹52,000 gives ₹36,400, and an HR letter built on that number will be wrong in your favour for exactly one conversation.

And to a sale price. If a listing says ₹1,999 after 33 percent off, the MRP was about ₹1,999 divided by 0.67, roughly ₹2,984, so the tag was probably ₹2,999 with the percentage rounded. Adding 33 percent to ₹1,999 gives ₹2,659, which is not what the tag said.

The calculator has no reverse mode because it does not need one: type the percentage in A and the total in B, take “A% of B” to get the tax amount, and subtract. Or divide the total by (1 + rate) yourself; it is one step.

Two things it will not do. It will not compute a change from zero: there is no percentage that describes going from nothing to something, so it shows a dash and you should report the absolute number. And it will not average percentages for you, because a 10 percent gain followed by a 10 percent loss is a 1 percent loss, not zero; for anything involving growth over several periods the compound interest calculator is the right tool.