The cost of some train tickets could be almost 6% higher next year.
Rail commuters will be paying close attention to the announcement of last month's Retail Prices Index (RPI) figure today, as it will be used to calculate increases to next year's regulated fares, including season tickets.
Ticket price rises are capped at 1% plus the July RPI figure, expected to be around 2.6%.
Train companies can add another 2% to some fares, as long as the overall average remains as per the formula.
Campaigners say ticket prices are rising four times faster than the average wage and that the measurement used to calculate fare increases has been discredited.
Rail fares have been rising faster than the rate of inflation for more than a decade. So how do you make your money go the furthest by rail?
What could the impact of rail fare rises be on your wallet? Compare selected season tickets before and after the forecasted rise.