Work out any rise, forwards or backwards

Take the new value, subtract the old one, divide by the old value, then multiply by 100. Dividing by the new value instead is the single most common mistake — it gives a smaller, wrong answer. From 240 to 288: (288 − 240) ÷ 240 × 100 = 20%.

Yes. 100% of the original gets added on top of the original, so you end up with twice as much. Carrying on: a 200% increase gives three times the original, and a 900% increase gives ten times. This is why "a 200% increase" and "200% of the original" mean completely different things — the second one is actually a decrease if the original was larger.

Because the second rise is applied to the already-raised amount. Two 10% increases give 1.10 × 1.10 = 1.21, a 21% rise overall rather than 20%. The gap widens fast: three 10% rises come to 33.1%, and ten of them come to 159.4%. The "Repeated increase" tab shows the compounding period by period.

A 42.86% rise, not 30%. The fall is measured against the original figure but the recovery is measured against the smaller one left behind. The formula is D ÷ (100 − D) × 100. A 50% fall needs a 100% rise, and a 90% fall needs a 900% rise. The "Recover from a drop" tab works this out for any fall.

Divide, don't subtract. A price of 276 after a 15% increase came from 276 ÷ 1.15 = 240. Taking 15% off 276 would give 234.60, which is wrong, because that 15% is being calculated from the larger figure. Use the "Original before the rise" tab for this.

Use a percentage increase when you're describing one jump between two points in time. Use a growth rate such as CAGR when the change happened across several periods and you want a figure that's comparable to other timespans. Revenue going from 40k to 72k is an 80% increase overall, but a 12.47% annual growth rate across five years — the same fact, framed for different audiences.