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Background: Obesity‐induced hypogonadism, which manifests as erectile dysfunction and a lack of libido, is a less visible and under‐recognized obesity‐related disorder in men. Objective: We examined the impact of weight loss on total (TT) and free testosterone (FT) levels, and constructed nomograms to provide an easy‐to‐use visual aid for clinicians. Materials and methods: Meta‐analysis was conducted using RevMan (v5.3) and expressed in standardized mean differences (SMD) for testosterone. Parallel‐scale nomograms were constructed from baseline and target body mass index values to estimate the gain in testosterone. Results: In total, 44 studies were included, comprising 1,774 participants and 2,159 datasets, as some studies included several datasets at different time points. Weight loss was controlled by low calorie diet (LCD) in 19 studies (735 participants, 988 datasets), by bariatric surgery (BS) in 26 studies (1,039 participants, 1,171 datasets), and by both in one study. The median follow‐up was 26 weeks (interquartile range = 12–52). The range of baseline mean age was 21–68 yr, BMI: 26.2–71.2 kg/m2, TT: 7–20.2 nmol/L and FT: 140–583 pmol/L. TT levels increased after weight loss by LCD: SMD (95%CI) = 2.5 nmol/L (1.9–3.1) and by BS: SMD = 7.2 nmol/L (6.0–8.4); the combined TT gain was 4.8 nmol/L (3.9–5.6). FT levels increased after weight reduction by LCD: SMD = 19.9 pmol/L (7.3–32.5) and by BS: SMD = 58.0 pmol/L (44.3–71.7); the combined gain was 42.2 pmol/L (31.4–52.9). Greater amounts of total and free testosterone could be gained by weight loss in men with higher baseline BMI, or lower levels of SHBG, TT and FT, while gain in TT was relatively greater in older and FT in younger age. Age‐stratified nomograms revealed that compared to older men (> 40 yr), younger men (≤ 40 yr) gained less TT but more FT for a given weight loss. Discussion and conclusion: Both TT and FT levels increased after weight loss, relatively greater with higher baseline BMI, or lower levels of SHBG, TT and FT. Nomograms constructed from a large number of participants with a wide range of BMI and testosterone values provide an evidence‐based and simple‐to‐use tool in clinical practice. [ABSTRACT FROM AUTHOR]