The mystery of when the cheapest train tickets will go up in price could be solved by a new online tool.
A price predictor launched by ticket retailer Trainline uses historical and current trends to inform passengers when Advance fares are likely to become more expensive.
Most operators release these tickets around 12 weeks before a journey but the price usually increases as demand grows and time passes, meaning it can be costly to delay purchases.
Passengers have previously been given little indication of how quickly they need to book to secure the best prices.
Trainline's chief product officer Jon Moore said: "Our data scientists have used historical pricing trends from billions of customer journey searches to predict when the price of an Advance ticket will expire.
"We now share this information in our app to allow our customers to get the best price possible for their journey.
"We're introducing more advanced machine learning every day so naturally our predictions will get increasingly accurate.
"Our mission is to make train travel as simple as possible and price prediction is the first in a long line of predictive features we have planned to help customers save time and money."
The firm said people who buy tickets on the first day they search for them save an average of 49% compared with walk-up fares.
The price predictor is available on the Trainline app, which also alerts passengers to which sections of a train are likely to have empty seats.
:: This is the typical price increase of a standard class Advance single from London Euston to Manchester Piccadilly departing on a Tuesday at 6.16am, according to Trainline:
£32 when bought 80 days before travel
£38 when bought 41 days before travel
£42 when bought 13 days before travel
£87 when bought two days before travel
£126 when bought on the day of travel