Mileage allowance over part of a year: prorate the period first
Compare an annual driving estimate with an allowance over 18 months without mixing periods.
Method
An annual mileage estimate and a total mileage allowance describe different periods. Before comparing them, put both on the same time basis. An annual estimate answers how far you might drive in one year. A total allowance answers how much distance is assigned to the full period. A straight-line calculation is useful for planning, but the actual agreement determines how an allowance is applied.
For a planning period measured in complete months, multiply an annual allowance by the number of months divided by 12. If the period uses exact dates instead, use the stated day-count rule rather than silently mixing a monthly rule with a 365-day annualisation. Keep kilometres and miles consistent. Converting only one side of the comparison creates an apparent shortfall that is a unit error.
- InputsDistance entered · Distance · Distance unit
- MethodAnnual distance = entered distance × active periods. The multiplier depends on whether the distance is daily, weekly, or monthly.
- ResultEstimated annual distance
Example only; replace these assumptions with your own values.
Worked example
An illustrative annual allowance of 15,000 km gives 22,500 km over 18 months under the simple monthly rule. If 14,000 km has been driven after 10 months, 8,500 km remains for the next 8 months. Dividing that remaining distance by 8 gives a planning pace of 1,062.5 km per month. It does not change the total allowance or guarantee that every future month will be equal.
Compare that remaining pace with your planned travel rather than relying only on the pace so far. The first 10 months averaged 1,400 km per month. Continuing at that pace for 8 more months would add 11,200 km and produce 25,200 km in total, which is 2,700 km above the illustrative allowance. A change in commute or a long trip can make the remaining period different from the past.
15000 × 18 / 12 = 22500 km
22500 − 14000 = 8500 km
8500 / 8 = 1062.5 km/month
14000 + 1400 × 8 = 25200 km
- Allowance
- 22500 km
- Projected distance
- 25200 km
- Projected excess
- 2700 km
15,000 × 18 ÷ 12 = 22,500; this example does not determine contract terms.
Checks and limits
Use Annual mileage for a driving estimate, then align its annual result to the comparison period. Record odometer readings and dates separately from estimates. Check the written allowance, excess-distance treatment and any partial-period rule before making a contractual decision. This example explains proportions only; it does not determine a contract’s terms or the amount of a charge.
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Source: OpenStax