shouldibuygastoday

Personalization

The decision tree

The models predict the market. A small decision tree turns that prediction into an answer for you, given your car, your commute, and how much gas you have left.

Why a tree?

A decision tree is one of the most interpretable classifiers in machine learning. Every answer can be traced back through a small number of yes/no questions, so when the site tells you to fill up, you can see exactly why. The market ensemble already produces a probability. The tree's job is the last mile, deciding what that probability means for someone with a quarter tank and a 30-mile commute.

Features it splits on

  • days_of_gasEstimated from your tank level, your car's combined MPG (EPA data), and your daily commute. The tree splits at 1, 3, and 7 days.
  • tank_levelCurrent tank percentage. A near-full tank (≥ 85%) short-circuits the tree to "wait" regardless of market. If there's nothing to fill, there's nothing to save.
  • market_buyThe ensemble's recommendation: YES or NO.
  • market_confidenceHow confident the ensemble is in that recommendation. Strong signals (> 0.6) are taken at face value; weak ones get second-guessed.
  • vibesExistential dread, 1–5. Mostly a tiebreaker: high vibes flip a borderline "wait" into a "fill up for peace of mind."

The tree

Ten leaves, max depth six. Hand-authored (not trained) because we have no ground-truth data on what users actually did after seeing a recommendation. Think of it as a rule set written in tree form, chosen for transparency over accuracy.

yesnoyesnoyesnoyesnoyesnoyesnoyesnoyesnoDays ≤ 1?Tank is effectively empty.BUYTank ≥ 85%?Tank is nearly full — there's no room to benefit.WAITDays ≤ 3?Market: buy?Market: buy?Low tank and prices are expected to rise.BUYLow tank — don't wait on a falling market.BUYMarket conf > 0.6?Days > 7?Market signal is strong.BUYVibes ≥ 4?Plenty of fuel and prices are expected to ease.WAITMarket says wait and your tank allows it.WAITWeak signal and you just can't deal right now.WAITWeak lean, but it's a quick errand while you're up for it.BUY

Limitations

  • Tank size is hardcoded at 14 gallons. Trucks and SUVs carry more; subcompacts carry less. A future version should pull tank capacity from the EPA dataset alongside MPG.
  • Commute is assumed to be the only gas use. Road trips, errands, and weather all change actual consumption.
  • The thresholds (1, 3, 7 days; 0.6 confidence; vibes ≥ 4) are author-picked, not learned. They're tunable in site/lib/decision-tree.ts.

Back to today's recommendation