Introduction Over 50% of people affected by cancer report unmet support needs. To address unmet information and psychological needs, non-government organisations such as Cancer Councils (Australia) have developed state-based telephone cancer information and support services. Due to competing demands, evidence of the value of these services is needed to ensure that future investment makes the best use of scarce resources. This research aims to determine the costs and broader economic and social value of a telephone support service, to inform future funding and service provision. Methods and analysis A codesigned, evaluative social return on investment analysis (SROI) will be conducted to estimate and compare the costs and monetised benefits of Cancer Council Victoria’s (CCV) telephone support line, 13 11 20, over 1-year and 3-year benefit periods. Nine studies will empirically estimate the parameters to inform the SROI and calculate the ratio (economic and social value to value invested): step 1 mapping outcomes (in-depth analysis of CCV’s 13 11 20 recorded call data; focus groups and interviews); step 2 providing evidence of outcomes (comparative survey of people affected by cancer who do and do not call CCV’s 13 11 20; general public survey); step 3 valuing the outcomes (financial proxies, value games); step 4 establishing the impact (Delphi); step 5 calculating the net benefit and step 6 service improvement (discrete choice experiment (DCE), ‘what if’ analysis). Qualitative (focus groups, interviews) and quantitative studies (natural language processing, cross-sectional studies, Delphi) and economic techniques (willingness-to-pay, financial proxies, value games, DCE) will be applied. Ethics and dissemination Ethics approval for each of the studies will be sought independently as the project progresses. So far, ethics approval has been granted for the first two studies. As each study analysis is completed, results will be disseminated through presentation, conferences, publications and reports to the partner organisations.

What is the economic and social return on investment for telephone cancer information and support services in Australia? An evaluative social return on investment study protocol