Although informal finance forms a large part of their financial sector, nearly all low income countries exclude informal transactions in official monetary data. Usually, informal finance data are nonexistent and occasionally, they are available only from surveys that often occur at irregular intervals and mostly with incomparable data. Using two survey datasets, indigenous knowledge, and elements of Friedman’s data interpolation technique, this study constructs monthly time series of informal credit and interest rates for Malawi. The study argues that datasets constructed in this manner may be used with minimal loss of substance in place of the actual but nonexistent data.