Systems and methods for lap timing and counting in athletic events are disclosed. The systems and methods do not require the athlete to wear a counter/timer, a transmitter, a reflector or another kind of marker. A portable computing device with a sensor, such as a tablet computer with a camera, is positioned in an appropriate location. Data from the sensor is transformed into a time series of data, and one or more learned statistics are calculated in real time as benchmark ambient conditions. The learned statistics are essentially continuously updated and data that indicates irrelevant volatility is excluded. A detection threshold is determined and essentially continuously updated based on the learned statistics, and lap completion is determined based on the threshold. Times, lap counts, and other data are displayed on the portable device in real time.
