New tool: a Farm Diesel Cost Calculator, and the VAT question most farmers get wrong

Another one for the farming tools. This works out what the diesel in your tractors actually costs you, per hour, per day, per month, per season and per hectare.

I went looking for an existing South African version of this before building anything and could not find one. What is out there is either an American tractor calculator working in gallons per acre and dollars, or one of the many South African trip fuel calculators built for a car on the N3. Nothing that knows a farm from a bakkie.

The gap that matters is the SARS diesel refund. A registered on land claimant gets 382,2 cents a litre back on eligible diesel, and since 1 April 2026 that is on 100% of eligible litres rather than 80%. At the current inland price that is about a seventh of what you pay. Budget a season at the price on the delivery note and every number you produce is roughly 15% too high. So the tool puts that on an explicit ladder, what you pay, what the refund takes off, what a litre really costs, and one switch moves every rand figure on the page between those two footings at once. That last part matters more than it sounds: a cost per hectare worked out before the refund and one worked out after it are not comparable, and mixing them is easy to do by accident.

The bit I got wrong first, and had to go and check properly. I was about to add a step netting VAT off the diesel price, on the reasoning that a VAT vendor claims input VAT on everything. You cannot. Diesel is zero rated for VAT in South Africa under section 11(1)(h) of the VAT Act, as a fuel levy good, specifically so it is not taxed on top of the fuel levy and RAF levy already in the price. There is no VAT in the diesel price, so there is nothing to claim back on it. What can carry VAT is a separately charged delivery or call out fee, and you claim that line in the ordinary way. Had I not checked, every figure on the page would have been flattered by about 13%. The ladder now shows that as an explicit zero rather than quietly leaving it out, because I suspect I am not the only one who assumed otherwise.

Two ways to use it. The first tab turns a burn rate into costs, either from litres an hour you have measured yourself, which is always the better number, or estimated from your tractor kilowatts and the job. It also works out what gearing up and throttling down would save you, and, just as usefully, tells you when it would not: not while ploughing, and never on a baler or mower conditioner, since those need the engine held at PTO speed.

The second tab builds a whole season pass by pass, knifing in fertiliser through to combining, and adjusts every tillage figure for your soil. That adjustment is not a rounding detail. Primary tillage on clay takes something like 35 to 45% more diesel than the same job on loam, which is most of the Highveld, so leaving it on the default is the biggest single error you can make on that tab.

Alongside it are the Cedara tillage trial figures, which are properly South African: 53,4 litres a hectare to establish maize conventionally with a disc, plough and disc, against 20,3 litres a hectare under no till. Before anyone reaches for the ripper on the strength of that, read the rest of that trial, and I have put the caveat directly under the table rather than in a footnote. The no till treatment needed a glyphosate spray and an extra 40 kg of nitrogen a hectare, and once those were counted the total establishment cost came out much the same. The fuel saving is real. The cost saving was not. Diesel is one line in the budget, not the budget.

On sourcing, since a few of you have asked about this on previous tools: litres per hour comes from the ASABE D497 model, cross checked against the fuel rule in the Department of Agriculture’s own Guide for Machinery Costs, and the two agree closely once you put them on the same footing. The field capacity formula and the Highveld altitude note, that a naturally aspirated engine delivers only about 80% of its rated power up here, come from that same guide. The litres per hectare per operation table is published in a South African text but the underlying survey was done in Nebraska, so it is labelled indicative rather than local, and it says so on the page.

What I would most like from anyone farming: check the litres an hour against your own fuel records, and the season total against what you actually burned last year. A conventional maize programme comes out around 64 litres a hectare on loam, which sits close to the roughly 60 litres a hectare Grain SA gives as typical, but a number that is right on average can still be wrong for your soil and your implements. If it is out for you, I would rather hear it and fix it.

Ja this one I can actually use. The refund side is where most okes get it wrong, they think its VAT they claiming back but its the fuel levy portion, and only for the on land farming use. Diesel you burn driving to town or in the private bakkie doesnt count. Keep your logbook properly or SARS will disallow the lot when they audit, I seen it happen to a neighbour and it was a expensive lesson.

Per hectare is the number that matters for me. Once you see what a ripping pass costs in fuel you start asking if you really need it every year. Will run my planter numbers through it this week.

The SARS refund piece is exactly what KZN sugarcane farmers have been talking about for years, because the diesel volumes those estates burn through in cutting season make even a few cents per litre add up to something significant across the whole season. A tool that puts the refund on an explicit line, rather than buried somewhere in the back of a spreadsheet that only the accountant looks at, is going to matter most to the smaller operators who are managing that number themselves. Does it handle more than one implement running in the same operation, or is it built around a single tractor pass at a time?

Good question, worth answering properly.

The second tab, Whole season by operation, is built exactly for that. It is not one implement at a time, you add as many passes as you need with the Add another pass button, each with its own operation picked from the list, its own hectares, and how many times you run it, and it totals the litres and cost across all of them. The four preset chips, Conventional maize, Reduced till maize, No-till maize and Hay cut, load a typical sequence, ploughing through to combining, that you then edit to match your own programme, add a pass, drop one, change the hectares per block.

What it does not do is model two implements running together in a single pass, a combined seeder and fertiliser rig for example. Each row draws its litres per hectare from a fixed list of 22 named operations rather than a free-text field, so a combined rig has to go in as whichever single operation on the list is the closer match, which is an approximation rather than something the tool works out for you. If that is common on the estates you are thinking of, I would like to know, it is the kind of gap worth adding proper support for rather than leaving as a workaround.

The first tab, Per hour and per day, is the single pass you mention as the alternative, useful for a quick “what does this afternoon’s spraying cost me” number. The season total lives on the second tab.

The 382,2 cents per litre refund moving to 100% of eligible litres from April is genuinely news to me, I had no idea the threshold changed from the old 80%. My brother-in-law runs a few hundred hectares outside Ventersdorp and I’d bet my DStv bill he’s still budgeting at the old rate. Sending this link across now.

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That VAT refund business is why you need an accountant worth his salt, because SARS changes these things quietly and half the farming community doesn’t hear about it until two years later. I’ve seen it happen with electrical contractors too, everyone still filing the old way because nobody told them different. The 80% to 100% threshold change is proper money though, especially if your brother-in-law’s running a few hundred hectares. Those litres add up fast when you’re doing full season passes. I’d be checking the fuel supplier invoices as well because sometimes there’s discrepancies there that get missed. A tool that puts it all in one place is sensible, saves you hunting through receipts and last year’s notes at the end of the season when you’re knackered.

Thanks Mark, appreciate the kind words.