Train companies should review the way they measure punctuality to better match passengers' satisfaction levels, a watchdog has suggested.
Punctuality is measured at present by arrival times at final destinations, rather than stops along the route.
A Passenger Focus study found commuters became less satisfied after a minute's delay, while it was 4-6 minutes for business and leisure passengers.
The train operators' association said firms worked hard to boost punctuality.
For train companies, a train is considered on time if it arrives at its final destination within 10 minutes of the scheduled arrival for long-distance operators and five minutes for shorter distance trains.
While trains can be late along a route, they can make up time towards the end of journey and still arrive on time.
However, evening commuters frequently disembark before the final destination, Passenger Focus said.
It compared results from its own twice-yearly National Passenger Survey with the Public Performance Measure, which records individual train performance against the planned timetable.
Passenger Focus looked at three companies over a three-four year period: 7,066 journeys on National Express East Anglia, 2,075 on Northern Rail and 4,997 on CrossCountry.
It matched individual passenger survey responses with the specific journey.
It recommended that companies review how they record train times, including punctuality along a route, rather than just the final arrival time.
Passenger Focus chief executive Anthony Smith said: "Punctual trains equal happier passengers. The good news is that the industry's current measure shows that punctuality is getting better with more trains running on time.
"However, our research shows that punctuality is still one of passengers' top three priorities for improvement. Perhaps now the point has come to explore further how the industry and passengers define 'on time' trains?"
In its most recent National Passenger Survey, Passenger Focus reported that more than four out of five railway passengers were satisfied with their journey.
Its annual survey of 31,000 rail travellers said 84% were satisfied, the highest since it started in 1999.
The Association of Train Operating Companies said the measure was similar to ones used abroad, and it was regularly reviewed.
"Train companies devote a great deal of energy and resources to making sure that more services arrive on time, and are acutely aware of how important punctuality and reliability are to passengers," a spokesman said.
"Significant improvements have been made over the last few years. But train companies are not complacent.
"As private sector operators, they want to keep their customers happy and will keep on working hard to continue to improve punctuality and provide passengers with the service they expect and deserve."