The letter usually arrives with a single number in it. Fifteen per cent, twenty, twenty-five. It names diesel, mentions drivers, sometimes attaches a news cutting, and asks for the new rate from the first of next month.
There are two easy answers and both are expensive. Saying yes pays for things that did not happen to your lane. Saying no to a carrier whose costs genuinely rose gets you older trucks, slower replies and, eventually, a declined booking on the day you need it most.
The better answer takes an afternoon and a spreadsheet. It turns one percentage into a set of separate claims, each of which can be checked, and it ends with a reply that has numbers in it rather than adjectives.
One percentage, four different claims
A rate increase request is almost always a blend of four things, and each one has its own evidence.
| The claim | What would prove it | Who can check it |
|---|---|---|
| Our costs have risen since the rate was set | Input prices on two dates, weighted by each cost's share | You, from public data |
| Your job has changed | Waiting time, drops, load size, payment days against what was quoted | You, from your own records |
| The market has moved | A published freight price series for the matching vehicle | You, from public data |
| The rate was never enough | Nothing public. Only the carrier's own numbers, or other quotes | Only by asking the market |
A single percentage hides which of these it is. The first job is to pull them apart, because the right response to each is different. A cost claim is paid by formula. A job-change claim is often fixed more cheaply at your own dock. A market claim is negotiated. A "never enough" claim is a real conversation that should not be disguised as a fuel story.
Test 1: find the date the rate was set
Every cost claim is a comparison between two dates, and the letter usually chooses the first one for you. It should be the date your current rate was agreed, not last month and not the carrier's own reference point.
The date matters more than most buyers expect, because Thai diesel has moved in steps over the past eighteen months. Monthly Bangkok averages, in baht per litre:
| Month | Diesel |
|---|---|
| May to September 2025 | 31.94 |
| December 2025 | 30.81 |
| February 2026 | 29.94 |
| March 2026 | 32.12 |
| April 2026 | 44.13 |
| June 2026 | 39.25 |
| 24 September 2026 | 41.44 |
The same letter, sent today, is justified by very different amounts depending on when your rate was last set. The table below uses a 10-wheel truck, weighted as in Test 2.
| Rate last set | Diesel then | Change to 41.44 | Fuel's share of cost then | What fuel justifies |
|---|---|---|---|---|
| Mid 2025 | 31.94 | +29.7% | 40.5% | +12.0% |
| February 2026 | 29.94 | +38.4% | 38.9% | +15.0% |
| April 2026 | 44.13 | -6.1% | 48.4% | -3.0% |
That last row is not a trick. A rate agreed in the April spike was agreed at a diesel price higher than today's. On fuel alone, it is due to come down.
Watch for the reference date written into the letter. When the national land transport federation announced a stepped increase from 1 April 2026, starting at 10%, it referenced a starting diesel price of 29.94 baht, which is the February 2026 average. That is a fair base for a rate set in February. It is the wrong base for a rate set at 31.94 in mid 2025, and a badly wrong one for a rate agreed in April.
Test 2: weight each cost by its real share
A diesel rise does not raise a rate by the same percentage, because fuel is only part of what a truck costs. The justified increase is each cost's share multiplied by how much that cost moved, added up.
Justified increase = (fuel share Γ fuel change) + (labour share Γ labour change) + (ownership share Γ ownership change) + (running share Γ running change) + (other share Γ other change)
The shares are the part everyone guesses. A carrier will usually tell you fuel is "about half". The Department of Land Transport's cost study gives a checkable starting point, built line by line for a representative operator at the diesel price of the day it was done, 24.99 baht in May 2017:
| Vehicle | Cost per km | Fuel | Driver and assistant | Vehicle, registration, insurance | Tyres, oil, repairs | Tolls, office, other |
|---|---|---|---|---|---|---|
| 4-wheel pickup | 8.25 | 28.2% | 41.3% | 13.7% | 9.5% | 7.0% |
| 6-wheel, consumer goods | 12.66 | 29.8% | 33.2% | 21.8% | 9.7% | 5.6% |
| 10-wheel | 17.61 | 34.8% | 23.9% | 28.6% | 8.7% | 4.1% |
| 18-wheel semi-trailer | 20.79 | 42.9% | 16.4% | 23.2% | 13.2% | 4.3% |
Three things come out of this.
The fuel share depends on the vehicle. The federation's stated figure of 40% to 45% of total cost matches the heaviest vehicles. For a pickup, the driver is the largest line and fuel is barely more than a quarter. The same diesel move justifies very different increases on different parts of your fleet.
The fuel share rises when diesel rises. At 24.99 baht, fuel is 34.8% of a 10-wheeler's cost. Re-price only the fuel line to 31.94 and it becomes 40.5%; at 44.13 it is 48.4%. So use the share as it stood on the date your rate was set. A share measured after a spike, applied to the change that caused the spike, counts the rise twice.
The study's other lines are at 2017 prices. Wages, trucks and parts have all moved since then, which means re-pricing fuel alone slightly overstates fuel's share today. If anything, that errs in the carrier's favour, which is the right direction for a test you want them to accept. If the carrier will show you its own cost split, use it instead. If it will not, this is a defensible default.
Test 3: take out what has already moved
Before adding anything up, remove the parts that have already been paid for, or that did not move at all.
- Fuel paid through a fuel clause. If your contract already has a fuel clause that has been adjusting the rate since April, the fuel part of the request has been paid. A request that includes it again is asking twice. How to tell a sound fuel clause from a weak one is in how fuel surcharges work here
- The trucks already on your lane. The vehicle line is mostly purchase cost written down over the truck's life, and a truck bought before your rate was set costs the same instalment today. That line is zero unless the carrier has replaced vehicles or renewed insurance at a higher premium, and either shows up on a document it can send you
- Labour, without evidence. The Ministry of Commerce named a shortage of skilled truck drivers among the reasons freight prices rose in the second quarter of 2026, so the claim is plausible. It is still a claim about this carrier's payroll. Ask for the driver cost per month, then and now. A headline wage announcement is not evidence of what a particular carrier pays
A worked example
A 10-wheel lane. The rate was agreed in mid 2025, when diesel sat at 31.94. The letter asks for 25%.
Start with the cost split on the date the rate was set, from the 10-wheel line above with fuel re-priced to 31.94. Then apply what each line has done since, using only what the carrier has shown you. Suppose it sends a payroll summary showing driver cost up 8% and workshop invoices showing tyres and repairs up 10%.
| Cost line | Share when the rate was set | Change since | Contribution |
|---|---|---|---|
| Fuel | 40.5% | +29.7% (31.94 to 41.44) | +12.04 |
| Driver and assistant | 21.7% | +8%, from payroll | +1.74 |
| Vehicle, registration, insurance | 26.0% | none shown | 0 |
| Tyres, oil, repairs | 8.0% | +10%, from invoices | +0.80 |
| Tolls, office, other | 3.8% | none shown | 0 |
| Justified | 100% | +14.58, or about 14.6% |
Fourteen point six, against twenty-five asked. The gap is 10.4 points, and the carrier has not yet said what it is for.
Now suppose the contract has a working fuel clause. The fuel row has already been paid, and the justified increase to the base rate is 2.5%. Same letter, same truck, same diesel. The number that matters depends entirely on what the contract already does.
Test 4: check it against what the market did
The formula tells you what the carrier's costs justify. The published road freight index tells you what freight prices actually did.
Between the second quarter of 2025 and the second quarter of 2026, the Ministry of Commerce index rose 11.1% overall, 11.3% for trailers and 12.0% for pickups. Diesel averaged 31.96 baht in the first of those quarters and 41.50 in the second, a rise of 29.9%. So across the market, freight prices moved by a little over a third of the diesel percentage, which is roughly what the fuel share predicts and nowhere near the full diesel move.
Two cautions when you use it.
- Take both numbers from the same release. The index is revised. The second quarter of 2025 was first published at 112.8; in the 2026 release the same quarter reads 111.7, and the weight given to pickups moved from 55.41% to 57.97%. Mixing releases can invent a point or more of "movement" that never happened
- A cost-based number is a ceiling, and the market often pays less. In its outlook for the third quarter of 2026, the Ministry of Commerce expected prices to stay high but noted that some operators may absorb higher costs to keep customers. The worked example's 14.6% assumes the carrier recovers every baht. The market, on average, recovered less
How to pick the index line that matches your goods and your vehicle, and how to budget around it, is covered in budgeting transport when rates are going to move.
Test 5: ask whether the job itself changed
Some of the gap is often not about prices at all. If your trucks now wait two hours at the gate instead of forty minutes, if the drop count per trip crept up, if the average load fell while the truck stayed the same size, or if payment slipped from 30 days to 60, the carrier's cost per job rose without any input price moving.
Check your own records against what the rate was quoted on. Where the cost came from your side, fixing it is usually cheaper than paying for it, and the carrier will often prefer the fix. The operating reasons a job becomes unattractive to a carrier, and the free ways to reverse them, are set out in why a carrier turns your job down.
Test 6: the rate that was never enough
After Tests 1 to 5, what is left is either unexplained or a claim that the rate was too low from the start. That can be true. A rate won in a competitive tender, or held flat for three years, may never have covered the lane properly.
No public data proves it either way, and it should not be smuggled in as fuel. There are two honest ways to test it.
- Ask the market. Two quotes for the same lane, on the same written brief, tell you whether the current rate is below what others would charge
- Look at the service you are getting. Declined bookings, substituted vehicles and slow confirmations on one lane are what a carrier losing money on that lane does, long before it writes a letter
If the rate was genuinely low, pay the correction deliberately, as a named line, once. That is a different decision from a fuel increase and should be recorded as one.
How to answer
Reply in writing, with the calculation attached, and split the answer into parts rather than giving one counter-offer.
- The justified cost increase, accepted, from a stated date. Show the shares, the two dates and the two prices. A carrier can argue with a number in a table. It cannot argue with "that seems high"
- Fuel moved into a clause going forward, with a named published price, a base price, a fuel share and a review frequency, so the next diesel move is settled by formula instead of by letter, in both directions
- The unexplained remainder, sent back as a question. Ask what it is for. If the answer is waiting time, drops or payment terms, offer the operational fix first
- A price-review procedure written into the contract. How often, against which data, with how much notice. Asking bidders to state this at tender stage is standard advice and is rarely done, which is why the letter arrives as a surprise
Do not aim to win by as much as possible. A rate pushed below the carrier's cost on your lane does not stay there; it shows up as the oldest truck, the least experienced driver and the booking that gets declined in the peak.
What to do this week
- Find the date your current rate was agreed, and the diesel price that month. That is the only base that belongs in the calculation
- Write down the vehicle type and take the matching cost split from the table above, with fuel re-priced to that month's diesel. Ask the carrier for its own split and use it if it gives one
- Check whether a fuel clause is already moving the rate. If it is, remove fuel from the request before doing anything else
- Set the vehicle line to zero unless the carrier sends a replacement purchase or an insurance renewal
- Ask for payroll and workshop evidence for the labour and running lines. Apply only what is shown
- Compare the result with the index for your vehicle over the same quarters, from one release
- Pull your own waiting, drop and payment data for the lane and see whether the job changed
- Reply with a table: accepted now, moved to a clause, and a question about the rest
A rate increase is not a negotiation about whether costs went up. They usually did. It is a negotiation about how much, since when, and whose costs they were, and all three have answers you can look up.