Practical guide
Pro rata temporis in fleet insurance: how the premium is calculated
Pro rata temporis spreads the full annual premium over the period a vehicle was actually covered. Five calculation conventions coexist and give different amounts for the same period: the one in your contract is set out in the special conditions of your policy.
Definition
When a vehicle enters or leaves the fleet during the year, its premium is calculated in proportion to the period covered: full annual premium multiplied by the share of the year retained.
The way that share of the year is counted is the prorata convention.
The five conventions
ACT/365: actual days, 365 day year. ACT/360: actual days, 360 day commercial year. 30E/360: 30 day months, 360 day year.
Started months: any month started is charged in full. Fortnights: any half month started is charged in full.
Where to find your contract's convention
In the special conditions of your policy. If they do not name it, ask your broker; the checker also lets you find the one that gives the amount charged.
Worked example: CHF 325.- from 26.08.2025 to 31.12.2025
Full annual premium of CHF 325.- for the period from 26.08.2025 to 31.12.2025 inclusive. The amounts below are calculated by the checker's engine.
- Convention
- ACT/365
- Definition
- Actual days, 365 day year.
- Units
- 128 units out of 365
- Amount
- CHF 113.97
- Convention
- ACT/360
- Definition
- Actual days, 360 day commercial year.
- Units
- 128 units out of 360
- Amount
- CHF 115.56
- Convention
- 30E/360
- Definition
- 30 day months, 360 day year.
- Units
- 125 units out of 360
- Amount
- CHF 112.85
- Convention
- Started months
- Definition
- Any month started is charged in full.
- Units
- 5 units out of 12
- Amount
- CHF 135.42
- Convention
- Fortnights
- Definition
- Any half month started is charged in full.
- Units
- 9 units out of 24
- Amount
- CHF 121.88
| Convention | Definition | Units | Amount |
|---|---|---|---|
| ACT/365 | Actual days, 365 day year. | 128 units out of 365 | CHF 113.97 |
| ACT/360 | Actual days, 360 day commercial year. | 128 units out of 360 | CHF 115.56 |
| 30E/360 | 30 day months, 360 day year. | 125 units out of 360 | CHF 112.85 |
| Started months | Any month started is charged in full. | 5 units out of 12 | CHF 135.42 |
| Fortnights | Any half month started is charged in full. | 9 units out of 24 | CHF 121.88 |
In this example, the amount ranges from CHF 112.85 to CHF 135.42 depending on the convention, a difference of CHF 22.57 on a single line.
Check a line of your statement with the prorata checker
Prorata checker
Enter the full annual premium and the covered period. The five Swiss market conventions are calculated, and the invoiced amount is compared with each of them.
Enter a premium and a period. The five Swiss market conventions are calculated in your browser, no data leaves it.
- ACT/365
- Units
- 128
- Denominator
- 365
- Amount
- CHF 113.97
- ACT/360
- Units
- 128
- Denominator
- 360
- Amount
- CHF 115.56
- 30E/360✓
- Units
- 125
- Denominator
- 360
- Amount
- CHF 112.85
- Started months
- Units
- 5
- Denominator
- 12
- Amount
- CHF 135.42
- Fortnights
- Units
- 9
- Denominator
- 24
- Amount
- CHF 121.88
| Convention | Units | Denominator | Amount |
|---|---|---|---|
| ACT/365 | 128 | 365 | CHF 113.97 |
| ACT/360 | 128 | 360 | CHF 115.56 |
| 30E/360✓ | 125 | 360 | CHF 112.85 |
| Started months | 5 | 12 | CHF 135.42 |
| Fortnights | 9 | 24 | CHF 121.88 |
Maximum difference
CHF 22.57
that is 20 percent between the most and least expensive convention for this period.
Your insurer applies the 30E/360 convention.
Have your statement recalculated
We match each line of the statement against your contract's convention, once, free of charge and with no commitment.
Frequently asked questions
Further reading
Flottaris gives no insurance advice and disputes nothing on your behalf. The rules that apply are those of your policy; your broker remains your contact.