Alimi, Maruf O.Usman-Hamza, Fatima EnehezeiMustapha, I.OOgidan, Bolaji2019-10-152019-10-152018-05http://hdl.handle.net/123456789/2448Software reliability determination during design stage will be of immense benefit to all forms of software product development as any function expected of the software that cannot be solved shows where rework or recoding will be necessary and improve its reliabilityFlawless software with 100% functionality, reliability, compatibility, and flexibility is not yet available. Many researchers, software developers, and software engineers have tried their best, but yet are to produce a perfect software system. This research attempts to derive a model that can be used to make software more reliable at the design and development stage. Reliability formula was derived using existing serial and parallel reliability formula as applied to modular systems of software development. For better error prevention than rework, functionality profile of modules was suggested and was used to calculate reliability with minimum acceptance level for critical and non-critical systems. With these reliability formulas, if fully implemented will enhance the productivity and reliability of software products.ensoftwarecritical systemsreliabilityserial-moduleArticle