Abstract: A method of calibrating a pump that is subject to variations in flow rate based on inlet pressure variations, such as a peristaltic pump found in medical instruments. The pressure at the inlet of the pump is measured and recorded during prior uses of the pump. A mean or average inlet pressure is derived from the measurements, either directly or indirectly from the measurements of using regression techniques, as a way of forecasting the inlet pressure during the next use of the pump. The pump is then calibrated at an inlet pressure that is set or adjusted to match the mean or average inlet pressure. The calibration is thus accurately performed for the pump, and is independent of the absolute accuracy of the inlet pressure sensor.