Methodology
Every number on this site is either official data with a timestamp or your own input — here's exactly how it works.
Where every number comes from
Two outside feeds and one source only you control:
| Source | What we use | Updates | Link |
|---|---|---|---|
| EIA Gasoline and Diesel Fuel Update | Weekly retail on-highway diesel, national + 5 PADD regions | Weekly: normally Tuesday around 10am ET; Wednesday after a Monday federal holiday | eia.gov/petroleum/gasdiesel |
| IFTA Inc. tax matrix | Diesel tax rates, 48 US member states | Quarterly rates, refreshed weekly | iftach.org/taxmatrix4 |
| Your inputs | Miles, costs, rates | Never stored — everything computes in your browser | — |
We check for EIA updates Tuesday through Thursday. Prices keep their Monday data date, and the site retains the latest verified average while newer data are unavailable or fail validation.
No login, no API key, no tracking pixel on what you type. Close the tab and the numbers you entered are gone.
Every formula on this site
Every calculator on DieselMath reduces to one of the lines below — no hidden multipliers, no rounding tricks. Click through to run it with the displayed data and your own inputs.
- Fuel cost: gallons = miles ÷ MPG · fuel cost = gallons × price per gallon
- Fuel surcharge: surcharge per mile = (current price − base price) ÷ MPG
- Cost per mile: fixed per mile = monthly fixed costs ÷ miles per month · variable per mile = (diesel ÷ MPG) + maintenance + tires
- Load profit: total miles = loaded + deadhead · profit = gross − (total miles × your cost per mile) − factoring fee
- Break-even rate: break-even per loaded mile = cost per mile ÷ (1 − deadhead %)
- Loan payment: payment = P × r(1+r)^n ÷ ((1+r)^n − 1), where P = financed amount, r = monthly rate, n = months
- Per-mile salary: weekly = rate × miles per week · annual = weekly × weeks per year · monthly = annual ÷ 12
- IFTA net tax: gallons burned in a state = miles in that state ÷ fleet MPG · net = burned × state rate − gallons purchased there × rate
- Factoring simple annualized fee: annualized fee (%) = fee (%) × 365 ÷ days you'd wait
- Fuel card savings: annual savings = gallons/week × discount × 52
What we simplify
No calculator captures every real-world variable in your business. Here's exactly where we drew the line, so you know what to check yourself before you rely on a number:
- IFTA surcharge states. Indiana, Kentucky, and Virginia each layer an additional per-gallon surcharge on top of their base IFTA tax rate. The estimator's net tax figure doesn't model that surcharge — budget extra if you run those states.
- DEF cost. Diesel exhaust fluid isn't included in any fuel-cost math on this site. DEF typically runs 2-3% of fuel spend; add it on top for a fully loaded number.
- Factoring advances, reserves and other charges. The calculator scales the entered fee on the invoice amount to a simple yearly percentage, and subtracts that fee from the invoice. It excludes advance amounts, reserve release timing, other charges and compounding; the results are not a financing APR or an up-front funding quote.
- Loan amortization. The truck payment calculator assumes a simple, fixed-rate amortization schedule. It doesn't fold in origination fees, balloon payments, or early-payoff penalties.
Corrections
Spot an error? Email corrections@bodhi.tools. We fix within a week and note the change here.