Let f and g be spectrally normalized holomorphic newforms of even weight \(k \ge 2\) on \(\Gamma _0(q)\) . If \(f\ne g\) , then assume that q is squarefree. For a nice test function \(\psi \) supported on \(\Gamma _0(1)\backslash \mathbb {H}\) , we establish the best known bound (uniform in k, q, and \(\psi \) ) for \( \int _{\Gamma _0(q)\backslash \mathbb {H}}\psi (z)f(z)\overline{g(z)}y^{k}\frac{dxdy}{y^2}-\mathbbm {1}_{f = g}\frac{3}{\pi }\int _{\Gamma _0(1)\backslash \mathbb {H}}\psi (z)\frac{dx dy}{y^2}. \) When \(f=g\) , our result yields an effective holomorphic variant of quantum unique ergodicity, refining work of Holowinsky–Soundararajan and Nelson–Pitale–Saha. When \(f \ne g\) , our result extends and improves the effective decorrelation result of Huang for \(q=1\) . To prove our results, we refine Soundararajan’s weak subconvexity bound for Rankin–Selberg L-functions.