Diesel Budget Buffer: Cents to Pad in a Quote

Why this matters. On Aug 31, 2026, the EIA weekly U.S. retail diesel price was $5.599 a gallon. Three weeks later, on Sep 21, it was $6.529. That is 93.0 cents in 3 weeks. A quote built on the Aug 31 price and fixed for those 3 weeks would have carried a 93-cent gap on every gallon. The question for a quote is how many cents to hold back.

A unit trap before the numbers

The EIA API returns prices as integer mills: dollars x 1,000 per gallon. A value of 6,199 means $6.199. One mill is a tenth of a cent. A rise of 1,376 mills is 137.6 cents, or $1.376 a gallon, which is $1,376 on 1,000 gallons. Mix this up and a buffer comes out 10 times too large or too small.

The 90th percentile by horizon

For every start week in the look-back, we measure the price change over the next 4, 8, 13 or 26 weeks, sort the changes and read off a percentile. The 90th percentile says: in 9 of 10 start weeks the price rose by no more than this.

Source: EIA open data API v2, retrieved Oct 10, 2026; nearest-rank percentile. Last column is our arithmetic: cents per gallon divided by 6.5 mpg, an invented fuel economy, from the unrounded 5-year figures.

The look-back matters. Ten years of history give a smaller buffer (50 cents over 13 weeks) than the last 5 years do. The last 52 start weeks alone give 189 cents over 13 weeks. A calm year makes the reserve look smaller than it should, which is why the tool tells you to repeat it each quarter.

The spread behind the 90th percentile

Over the last 5 years, diesel rose over the next 13 weeks in 47% of cases. The median 13-week change was -3 cents. The 90th percentile is 138 and the largest rise was 217 cents. The reserve exists for the right tail, not for the usual week.

Same EIA snapshot, 260 start weeks. The 50th and 90th percentiles and the largest rise are on the tool page; the 75th and 95th are the other two bars it shows.

One load, three horizons

Take a 500-mile load at 6.5 mpg. That is 76.9 gallons. The reserve is gallons times the buffer. The recovery share is the part of a price rise you expect to get back through a fuel surcharge or the rate. The 60% below is an example only, because we do not suggest a figure.

Invented load. Reserve = 76.9 gallons x buffer. Net = reserve x (1 - recovery share). Rounded to the cent once.

For a fleet, scale it the same way. Ten trucks at 9,000 miles a month and 6.5 mpg burn 13,846 gallons a month. At the 4-week buffer that is $5,054, or $2,022 after a 60% recovery. A month is not exactly 4 weeks, so read this as an order of magnitude.

What 93 cents in 3 weeks looks like

Back to the hook. The run from Aug 31 to Sep 21, 2026 was larger than the 5-year 90th percentile for 4 weeks (37 cents) and for 8 weeks (71 cents). It then eased.

Source: EIA weekly retail on-highway diesel, U.S., converted from integer mills (6,199 mills = $6.199). Changes are our arithmetic.

Match the horizon to the promise

• A 4-week quote needs the 4-week figure. A contract rate you cannot reopen for 6 months needs the 26-week one.
• Check what the surcharge recovers. A schedule with a high peg or a step table can leave part of a rise on you. Use the fuel surcharge check on one load.
• Use your own region. The 13-week 90th percentile runs from 116 cents in the Rocky Mountain region to 138 for the U.S., with the West Coast at 134 and the latest West Coast price at $7.229.

The latest U.S. price, for the week of Oct 5, 2026, is $6.199, down from $6.382 the week before. Do not treat that as a trend. It is one point in a series, and the buffer only says what the spread has been.

Common questions

• Is this my pump price? No. It is the EIA weekly retail average for the U.S. or a region, not your card discount or the index in your contract.
• Why dollars per 1,000 gallons? One cent a gallon is $10 on 1,000 gallons, which is easier to picture at fleet volume.

The diesel budget buffer tool does the sums for your own trucks, miles and mpg. To see what your last 20 loads actually recovered from fuel surcharge, send them to us.