Over 100 countries now require multinational corporations (MNCs) to annually disclose geographic breakdowns of their economic activities to tax authorities through country-by-country reporting (CbCR) to combat tax avoidance. We examine whether and how this mandatory private tax disclosure affects firms’ voluntary after-tax earnings forecasts. Using difference-in-differences and regression discontinuity designs to strengthen causal inference, we find MNCs are more likely to issue after-tax earnings forecasts after CbCR implementation. This effect is more pronounced for MNCs engaging in more tax avoidance prior to the policy adoption and for those experiencing an improvement in tax-related internal information quality following CbCR. Additionally, analysts’ after-tax earnings forecast accuracy improves post-policy adoption, especially among firms that increase forecast issuances. We further document an increase in the precision and disaggregation of earnings forecasts, and effective tax rate forecasts post CbCR. Our findings suggest that mandatory private tax disclosure leads to improved voluntary public disclosures, generating external benefits for capital market participants.