A method for regulating a vehicle's speed including the steps of: determining a horizon by means of position data and map data of an itinerary made up of route segments with length and gradient characteristics for each segment; calculating threshold values for the gradient of segments according to one or more vehicle-specific values, which threshold values serve as boundaries for assigning segments to various categories; comparing the gradient of each segment with the threshold values and placing each segment within the horizon in a category according to the results of the comparisons; and, for each segment within the horizon which is in a category indicating a steep upgrade or a steep downgrade, calculating the vehicle's final speed vend after the end of the segment, based inter alia on the entry speed vi to the segment; and determining the entry speed vi for said segment based on the calculated final speed vend for the segment, which determination is defined by rules for said segment's category, so that the vehicle's final speed vend is within the range defined by vmax and vmin for the vehicle's current reference speed vset, on the supposition that vi is determined within the same range; and regulating the vehicle's speed according to speed set-point values vref based on the entry speeds vi to each segment.