A travel assistance method that is performed by a computer including at least one processor is provided. The travel assistance method assists travel of a subject vehicle and includes: setting a start point and an end point of a route where the subject vehicle travels along a curve; assuming a triangle including the start point and the end point; setting a control point on each of two sides of the triangle to assume a quadrangle; calculating a route line accommodated in the quadrangle; and assisting the subject vehicle in traveling along the curve.