Gas Prices Going Down 2.5%? Percent Increase and Decrease Explained

Step by step

1. Headline: gas prices fell 2.5% this week
   Good news, says the headline: gas prices fell two point five percent this week.
2. Feel better?
   Feel better?
3. EIA: regular gas $4.354 a gallon (Oct 5, 2026)
   Here's the official number. The U.S. Energy Information Administration says regular gas is four thirty-five a gallon.
4. A year ago: $3.124 → up 39%
   A year ago, it was three twelve. That's up thirty-nine percent.
5. 15-gallon tank: about $18 more, every fill-up
   Fill a fifteen-gallon tank, and you pay about eighteen dollars more. Every single time.
6. News: Strait of Hormuz disruptions keep prices high
   News reports point to the Strait of Hormuz: tanker attacks and costly detours keep prices high.
7. −2.5% vs +39%
   Now, the math. That two point five percent drop barely touches a thirty-nine percent jump.
8. To get back to $3.12: fall 39%?
   So how much does gas have to fall to get back to three twelve? Thirty-nine percent?
9. $4.35 − 39% = $2.64: too low
   Nope. Falling thirty-nine percent from four thirty-five lands at two sixty-four. Way too low.
10. Percent change: measured from the start
    Here's why. A percent change is always measured from where you start.
11. Same $1.23 · bigger start → smaller percent
    Going up, the start was three twelve. Going down, the start is four thirty-five. Same dollar and twenty-three cents, bigger start, smaller percent.
12. $1.23 ÷ $4.35 = …
    The drop we need: one twenty-three out of four thirty-five...
13. ≈ 28%
    about twenty-eight percent.
14. At −2.5% a week: how long?
    Sounds better. But at two point five percent a week, how long is that?
15. Each week: × 0.975
    Each week, the price keeps ninety-seven point five percent of itself. Multiply again, and again...
16. 14 weeks in a row
    fourteen weeks in a row. More than three months of good-news headlines.
17. Rockets and feathers: up fast, down slow
    Economists have a name for this: rockets and feathers. Prices shoot up fast and float down slowly. Look at March: up nineteen percent in just two weeks.
18. On a test: percent of the new price → 0.975ⁿ
    On a test: the price went up one dollar twenty-three. As a percent of the new price, that's about twenty-eight point two percent. To get back, the price has to shrink to about seventy-two percent of today's. With two point five percent drops, point nine seven five to the n has to reach that, so n is fourteen weeks.
19. On a test, it looks like this
    On a test, it can hide like this.