Abstract Background Informal care, the health care provided by the patient’s social network is important in low income settings although its monetary value is rarely estimated. The lack of estimates of the value of informal care has led to its omission in economic evaluations but this can result in incorrect decisions about cost effectiveness of an intervention. We explore the use of contingent valuation methods of willingness to pay (WTP) and willingness to accept (WTA) to estimate the value of informal care provided to HIV infected women that are accessing antiretroviral therapy (ART) under the Option B+ approach to prevention of mother-to-child transmission (PMTCT) of HIV in Malawi. Methods We collected cross sectional data from 93 caregivers of women that received ART care from six health facilities in Malawi. Caregivers of women that reported for ART care on the survey day and consented to participate in the survey were included until the targeted sample size for the facility was reached. We estimated the value of informal care by using the willingness to accept (WTA) and willingness to pay (WTP) approaches. Medians were used to summarize the values and these were compared by the Wilcoxon signed-rank test. Results The median WTA to provide informal care in a month was US$30 and the median WTP for informal care was US$13 and the two were statistically different (p < 0.000). Median WTP was higher in the urban areas than in the rural areas (US$21 vs. US$13, p < 0.001) and for caregivers from households from higher wealth quintile than in the lower quintile (US$15 vs. US$13, p < 0.0462). Conclusion Informal caregivers place substantial value on informal care giving. In low income settings where most caregivers are not formally employed, WTP and WTA approaches can be used to value informal care. Clinical trial number NCT02005835 .