This study addresses the lack of knowledge in software continuous planning and development under the circumstance of multiple product categories, by expanding the focus of developing single product to managing product portfolios with different priorities. The paper investigates how software companies can achieve various benefits when dividing their product development practices into the Horizontal model with three horizons of growth. This approach allows the software companies to have different product development and planning practices inside the company, strengthening their positions in well-established businesses as well as creating growth in completely new businesses. Theoretically, the paper draws on the business literature of Horizontal model and on the literature of agile and lean software development. The empirical part is based on a case study with one of the leading Finnish software companies. Altogether 12 narrative interviews were held, involving people with various roles from product manager to chief strategy officer. The research results present the issues of continuous planning and continuous development with multiple business horizons.