Many supplier agreements allow prices to rise in line with a price index, which measures how prices change over time. One example is Statistics Norway's consumer price index (CPI).
The agreement sets the rules for calculating the increase. When a supplier uses the wrong index, starting date or calculation, you can end up paying too much on every invoice that follows.
In this first article, we look at three ways price adjustments go wrong—and how to prevent them.
Example 1: The wrong index
- Invoices
- 313
- Overcharged by
- 5.3%
- Total overcharged
- NOK 70,284
What happened
A large Norwegian company had an agreement for servicing its equipment. The agreement tied price increases to the consumer price index. In 2024 and 2025, the supplier used a different index, which rose faster.
Why it matters
The supplier therefore charged more than the agreement allowed. A small difference can be easy to miss. If the supplier uses that higher price to calculate the next increase, the error carries forward.
Example 2: The wrong starting point
- Invoices
- 4
- Overcharged by
- 0.8%
- Total overcharged
- NOK 11,085
What happened
A mid-sized Norwegian company rented its premises. The lease said the landlord should calculate rent increases by measuring how much the consumer price index had risen since October 2023.
The landlord used September 2023 instead. This added an extra month of price growth to the calculation, so the company received four quarterly rent invoices that were too high.
Why it matters
The landlord used the right index but the wrong starting month. That mistake carried through to each later calculation.
Example 3: The wrong calculation
- Invoices
- 11
- Overcharged by
- 0.6%
- Total overcharged
- NOK 7,521
What happened
A mid-sized Norwegian company bought security services. Its agreement combined two price indices to calculate the annual increase: one accounted for 75% of the calculation, and the other accounted for 25%.
For one service, this calculation allowed a price increase of about 0.7% in 2026. The supplier raised the price by about 6.4%.
Why it matters
To check the increase, you need to check how much each index changed and how the agreement combines them.
Watchdog's best practices for price adjustments
1. Set clear adjustment rules
- Name the exact price index.
- Define the starting month and year for the calculation.
- Set the date of the first price adjustment.
- Ask the supplier to show the calculation on each invoice.
2. Negotiate future adjustments
The starting price is only part of the deal. How prices rise over time also affects what you pay.
Apply part of the index change. Agree to use, for example, 80% of each increase. If the index rises by 5%, your price rises by 4%.
Keep the starting price for longer. Negotiate a fixed price for the first two to three years. Also agree to measure index changes from the end of that period, so the supplier cannot add the earlier increases later.
A lower increase leaves a lower starting price for the next adjustment. Over time, that difference adds up.