A rate increase took effect June 1 on my client's Ameren Illinois account. Their billing period runs May 22 to June 20. The entire bill was charged at the new higher rate. But 10 of the 30 days in the billing period were under the old rate. Shouldn't the bill be split between old and new rates?
Short billing period after rate change — which rate applies?
Yes — most tariffs require proration when a rate change occurs mid-billing period. The bill should be split proportionally: 10/30 at the old rate and 20/30 at the new rate. If Ameren billed the entire period at the new rate, the client overpaid for those 10 days. Check the Ameren tariff for rate change proration language — it's usually in the general terms and conditions section.
Rate change proration is standard practice but billing systems sometimes apply the new rate to the entire period for simplicity. The overcharge per billing cycle is relatively small — maybe the difference between old and new rates times 10 days of usage — but it affects every customer on that billing cycle. File the claim and cite the proration provision. This is a black-and-white error that utilities correct quickly.
Filed it. The 10-day overcharge at the new rate was $127. Small but principle matters — and it adds up across my other Ameren clients who had the same billing cycle.