Forecast your electric fleet charging budget: A transparent model

A charging budget forecast estimates your electric fleet’s expected charging costs for a future period. It connects planned mileage, energy demand, charging locations and the costs assumed at those locations. Good fleet software can provide the necessary input data; whether it also includes its own forecasting model is something to check when assessing your requirements.

A reliable budget makes its assumptions visible. You should be able to explain which part comes from previous charging sessions, which values are planned and where uncertainty remains. A variance then becomes a question you can answer later.

Start with clear planning boundaries

First define what your budget covers. Does it include only purchased charging energy, or also agreed time-based fees, recurring fixed costs and other charging-related items? Also record whether you consistently use net or gross values. Mixing price bases makes the result unusable.

Choose a period you can plan operationally. Vehicle numbers, working days and assignments are often more clearly known for the coming month than for the whole of next year. You can build an annual plan from monthly values and update it as new information becomes available.

Also separate measured values from estimates. A vehicle newly added to the fleet has no charging history of its own. Mark the provisional assumption and schedule a date to review it against actual data.

Connect mileage and energy demand

A simple model is: planned kilometres divided by 100, multiplied by the assumed energy demand per 100 kilometres. The measurement basis of that energy demand is crucial. Charging-session data and in-vehicle displays can represent different measurement points.

For a budget based on purchased charging energy, a consistent metric using assigned kilowatt-hours and the corresponding mileage is helpful. Both values must cover the same period and set of vehicles. Substantially different battery charge levels at the beginning and end of short periods can distort the allocation.

Use sufficiently long, representative periods and check for unusual circumstances. Holiday months, new routes or temporarily incomplete charging costs are not an ideal basis for simply carrying figures forward without explanation. Record these influences directly alongside the assumption.

Plan charging locations and additional costs separately

Allocate expected energy demand across the charging locations relevant to your fleet. The shares must add up to 100 per cent. For each share, record a transparent price assumption with its date and source.

Calculate additional items separately if they are not included in the kilowatt-hour price. This lets you see whether the forecast changes because of energy volume, the price assumption or other fees. Take care not to count the same item both within a historical blended price and as an additional cost.

Separate planning is worthwhile for several vehicle groups. A vehicle that regularly stays at a site and a vehicle with changing work locations may have different charging shares. There should be an operationally meaningful reason for how the groups are defined.

Worked example: A monthly budget from five assumptions

Fictional calculation, not a price recommendation: A fleet with 30 vehicles plans 2,000 kilometres per vehicle per month. A provisional purchased charging energy requirement of 22 kWh per 100 kilometres is assumed. This gives 60,000 kilometres and 13,200 kWh.

For this example, 70 per cent of the energy is budgeted at €0.32 per kWh and 30 per cent at €0.54 per kWh. All amounts use the same price basis. The calculation is:

• 9,240 kWh × €0.32 = €2,956.80.

• 3,960 kWh × €0.54 = €2,138.40.

• Planned energy costs: €5,095.20.

• Separately assumed additional charging costs: €180.

• Total planned amount: €5,275.20.

If ten per cent more charging energy is needed while shares and prices remain unchanged, the energy component rises to €5,604.72. With unchanged additional costs, this produces a scenario of €5,784.72. The extra €509.52 comes entirely from the higher energy volume.

This calculation method helps you answer follow-up questions. You can change each assumption individually and see its effect. The figures are deliberately chosen examples and make no claim about typical fleet costs.

Practical tool: An assumptions sheet for the forecast

For each plan, create a sheet with seven items: planning period, vehicle group, mileage, energy demand, charging shares, price bases and additional items. Add the source of every assumption, the person responsible and the next review date.

Include three scenarios suited to your operations: the expected outcome, higher energy demand and a changed distribution of charging locations. Change only factors you can explain. A blanket contingency margin without an explanation hides the uncertainty you are trying to represent.

After the month ends, attribute the variance to its causes. Were more vehicles active? Did assignments increase? Are any sessions still missing? Automated fleet reporting can provide a recurring framework for this. First check whether the fleet software data export includes the fields you need.

Use a sample period to clarify which information you need for your budget: discuss your fleet requirements with StromNow.