This study aimed to analyze the existing conditions and prediction of future carbon stocks in the planting of mangroves of the REMAJA PHE ONWJ program in Mekarpohaci Village, Karawang Regency, Indonesia. The observation began with the planting of 1200 seedlings of R. mucronata and A. marina, respectively. Furthermore, the monitoring of life graduation and diameter growth in the 2021-2023 period was carried out. Existing carbon stocks were analyzed by an allometric equation approach and carbon fraction values. Meanwhile, the prediction of future carbon stocks was modeled using Stella v.9.0.2 software concerning the growth rate of seedling stand diameter. The results of the study showed that carbon stocks reached 0.275 tons C in 2021, 3.66 tons C in 2022, and 5,765 tons C in 2023. Meanwhile, future carbon stock predictions indicate that the largest carbon stock in the 10-year growth projection is found in R. mucronata, with a value of 107.79kg C/tree, which includes 5.80kg AGC and 31.99kg BGC. In contrast, A. marina has the lowest carbon stock at 75.54kg C/tree (52.54kg AGC and 22.99kg BGC). The total contribution of carbon sequestration by 2033 is projected to reach 807.36 tons of CO2e, comprised of 474.69 tons of CO2e from R. mucronata and 332.67 tons of CO2e from A. marina.The carbon sequestration indicates that mangrove planting in the REMAJA PHE ONWJ program contributes to the reduction of CO₂ gas concentrations in the atmosphere and climate change mitigation and can realize the principles of sustainable development (SDGs).