The index of refraction for D2O at common wavelengths was measured for several temperatures at atmospheric pressure. While heavy water's refractive index was precisely measured decades ago using the transition lines of elements, those wavelengths are seldom used now that inexpensive lasers provide a range of available wavelengths. We review those measurements, note some inconsistencies between research groups, and fit the best of the literature data to a simple equation that allows an easy calculation for the refractive index of D2O with an accuracy of +/- 0.0002 at any visible wavelength and between (278 and 359) K. To verify the equation, we then compare the calculated refractive index to our measured values for three He-Ne laser wavelengths (543.5, 594.1, and 632.8) nm over a temperature range from (288 to 338) K and find good agreement.