How to calculate cost per job: six cells, petrol at R30

To calculate cost per job before the October fuel adjustment, build one Google Sheet with six input cells: petrol, other vehicle costs, electricity, water, medical aid and communication. Each cell carries its own date and source, and every job and open quote reads from them. It takes an afternoon and costs nothing but the time.

The six are not our invention. The Competition Commission's third Cost of Living Report, released on 4 September, named electricity, water, petrol, transport, healthcare and communication as costs rising faster than overall inflation. EWN's report on it gives electricity up 8.1% and water up 10.1% since July last year. Five of the six sit inside most service jobs, and a rate card escalated on one inflation figure under-recovers on exactly those five.

The hook is petrol. News of the Day reported on 22 September that petrol is "fast approaching R30 per litre" for October. The adjustment is due on Wednesday 7 October, CarMag reports, and every forecast so far would pass the June record of R28.06.

The forecasts disagree, and they have climbed all month. Stuff's reading of the Central Energy Fund snapshot of 10 September put 95 unleaded at R29.06, a rise of 214 cents. The Herald had inland 95 at R29.33 on 16 September, and The Witness had about R29.70 on 22 September. The sheet takes the official number on the day.

Before you start

• Three months of job cards showing the kilometres driven per job, or the vehicle logbook if the cards do not carry them.
• The fuel card statement per vehicle for the same three months.
• A list of every quote still open, with its validity date.

If the job cards carry no kilometres, that is step zero, and it is also the finding.

Step 1: Make an Inputs tab with six rows

Open a new Google Sheet and rename the first tab Inputs. Six rows and four columns: the line, the value, the date it was set, and where it came from. The source column is what makes the sheet defensible when a customer asks why the price moved.

Step 2: Fill the petrol cell from the official price

Enter the price per litre your vehicles paid this week, with the date. On 7 October replace it with the figure in the Department of Mineral and Petroleum Resources statement for that month. Its September statement is the format to expect. If part of the fleet runs on diesel, give diesel its own row rather than blending the two.

Step 3: Record litres per 100 km for each vehicle

A second tab, Vehicles, with one row per vehicle. Litres per 100 km comes from the fuel card and the logbook over three months, not from the brochure. A loaded bakkie in traffic rarely matches the manufacturer's figure, and the fuel card knows the real one.

Step 4: Put the other vehicle costs in the transport cell

Tyres, services, tolls and the licence, divided by kilometres driven, as rands per kilometre. It moves on its own dates, so keeping it apart from fuel lets each change show.

Step 5: Price the other four cells per billable hour

Electricity is the workshop's monthly bill divided by the hours it bills. Water is zero for most trades and real for anyone who washes, cleans or mixes. Medical aid is the employer's contribution per technician divided by billable hours. Communication is data and airtime per technician, on the same basis.

The medical-aid cell needs care. The Council for Medical Schemes' Circular 20 of 2026, published on 31 July, tells schemes to start their 2027 increases from projected inflation of 3.8%. The Board of Healthcare Funders has already called the figure unrealistic, Business Day reported on 23 September. Keep the current contribution in the cell, dated, until your scheme's own letter arrives.

Step 6: How to calculate cost per job from the cells

A Jobs tab with one row per job, holding kilometres, vehicle and hours from the job card. Fuel is kilometres times litres per 100 km, divided by 100, times the petrol cell. Transport is kilometres times the transport cell. The other four are hours times their cells, and labour and materials complete the total.

Take a 60 km callout in a bakkie using 12 litres per 100 km, as an illustration. That is 7.2 litres. The earliest forecast rise of 214 cents adds R15.41 to the job, and the Witness figure of 278 cents adds R20.02. On a maintenance contract quoted at 40 such callouts a month, that is R616 to R801 a month nobody priced.

Step 7: Reprice every open quote off the same cells

A Quotes tab, one row per open quote, costing its jobs from the Inputs tab exactly as the Jobs tab does. Add the validity date and filter for anything valid past 7 October. Those are quotes priced on September fuel and delivered on October fuel.

Step 8: Change a cell only with a new date and source

When a price moves, overwrite the value, the date and the source together, and every job and quote updates at once. Copy the old row to a History tab first. The next conversation with a customer can then show the move rather than assert it.

What breaks here

The 30-day quote that crosses the adjustment. A quote sent on 25 September and accepted on 20 October is costed on one price and delivered on the next. Either the quote states the fuel price it assumes, or the risk is yours.

The vehicle nobody logs. A pool bakkie driven by three people has no honest litres per 100 km, so its jobs are costed at a guess. Assign it to someone or log it.

The medical-aid line guessed from the guideline. The Council's 3.8% is guidance, not a cap, and a scheme may go higher if it can justify it. Wait for the scheme's letter.

When this stops being enough

The Sheet works for one person and a few dozen jobs a month. It fails when kilometres and hours are retyped from paper cards, because every retype is a day late and some are wrong. Past four or five vehicles, the cells are right and the job rows are not.

The connected version reads kilometres and hours off the job card that carries its own costs, and prices the open quotes in the sales pipeline off the same six inputs. One changed cell then reprices both. For a South African service business that join is what Zorah builds, starting from the fuel card and job records it already keeps.

On Monday, list every open quote valid past 7 October and add a column stating the petrol price each one assumed. The ones with no answer are the first to reprice.