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Tariff formula

The estimator on the Tariffs & estimator page computes a low–high range from the tariff table in src/data/tariffs.json. The formula is documented here so a buyer can audit it or replace it with their own.

Inputs

  • teu — number of TEU (1–500).
  • size — container size, one of 20, 40, 45.
  • type — cargo type, one of dry, reefer, tank, oog.
  • dwell — dwell days alongside (1–30).
  • terminal — terminal slug, used to look up the per-terminal surcharge.

Formula

base           = perTeu[size][type] × teu
reeferSurcharge = (type == 'reefer') ? reefer.perDay × dwell × teu : 0
dwellSurcharge  = max(0, dwell − freeDays) × dwell.perTeuPerDay × teu
subtotal        = base + reeferSurcharge + dwellSurcharge
terminalAdj     = subtotal × terminalSurcharge
mid             = subtotal + terminalAdj
low             = mid × (1 − uncertaintyBand)
high            = mid × (1 + uncertaintyBand)

Constants from tariffs.json

  • freeDays = 5 (free dwell period before surcharge applies)
  • reefer.perDay = USD 22
  • dwell.perTeuPerDay = USD 8
  • uncertaintyBand = ±12% (covers variable handling conditions)

Replacing the formula

The estimator logic lives in src/components/Estimator.astro — both the server-side default estimate and the client-side interactive recompute use the same estimate() function. To replace the formula, edit estimate() in both places (or extract it into src/lib/tariff.ts if you want a single source of truth).

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