This paper discusses the development of design charts for creep-fatigue evaluation using an integrated elastic-perfectly plastic analysis (EPP) and Simplified Model Test (SMT) approach. The creep-fatigue damage evaluation approach in current ASME Section III, Division 5 rules requires separate evaluation of creep and fatigue damages and then considers the effect of creep-fatigue interaction with a creep-fatigue interaction diagram, also known as D-diagram. The EPP+SMT approach avoids the use of D-diagram by directly comparing the strain range determined from an EPP analysis with design charts, conceptually developed directly from creep-fatigue and SMT tests, to determine the creep-fatigue damage. The EPP+SMT approach provides much simpler creep-fatigue design evaluation process compared to current methods and is also expected to reduce the over-conservatism in current methods. Generating the EPP+SMT design charts requires extrapolating high strain range, short hold time test data to low strain range and long hold times, typically experienced by structural components in high temperature nuclear service. This work investigates several extrapolation approaches in the development of methodologies for constructing EPP+SMT design charts for Alloy 617 at temperatures between 800°C and 950°C. The design charts are validated using failure data from pressurized SMT tests and by comparing the EPP+SMT method with current design methods for representative high temperature nuclear reactor components.