A method for manufacturing a layered paper or board web, in which method thick stock (M) delivered to the paper machine is diluted with tail water and the diluted stock (M1) is fractioned in order to produce two different stock fractions (A,B). The first stock fraction (A), with finer material, is conducted into the surface layer or layers of the web, and the second stock fraction (B), containing coarser material, is conducted into the middle layer or layers of the web. Before feeding into a headbox (15), the coarse stock fraction (B) is diluted with water whose consistency is substantially lower than the consistency of the water added into the thick stock (M) before fractionating. When water containing less solids than the normal tail water dilutes the coarse stock fraction, the stock fractions used for different web layers can better maintain their different properties, which improves the result of layering.