Metro's consistent ability in recent years to meet punctuality targets set by the state government is mostly achieved by running trains on time outside of peak hour and on weekends when the system is much quieter.

But Melbourne's rail operator falls short of its 88 per cent punctuality target in the morning peak when the network is busiest, and scrapes across the compensation threshold in the evening peak, leaked internal records show.

The documents reveal in extensive detail Metro's performance on every suburban line between March 1 and 7, the first week a new automated system was used to measure the company's performance.

Metro ran just 85 per cent of trains on time in the morning peak that week, and 89 per cent of afternoon peak services were punctual.

By contrast, it ran 95 per cent of trains on time on Saturdays and Sundays when patronage is lower and services are less frequent, helping the company to avoid paying out customer compensation to monthly and yearly myki pass holders.