As the world is transforming towards the development and utilization of low-carbon materials and construction techniques, early-age carbonation curing to store CO2 in the concrete is progressing. To calculate the amount of CO2 stored in concrete, it is important to measure the degree of carbonation and carbonation depth of the specimens. Researchers have previously used Thermo-Gravimetric analysis to measure the amount of calcite formed after carbonation. However, since the equipment is expensive, it is difficult to apply thermal analysis for regular quality control of the amount of CO2 stored in specimens. Since carbonation reduces the pH of concrete, historically, carbonation depth has been measured simply by spraying 1% phenolphthalein solution on the specimen. However, the relationship between carbonation depth and the amount of CO2 stored in concrete has not been investigated in detail. In this study, mortar specimens with W/C = 50% were first seal cured followed by carbonation curing at 80% CO2 concentration. Further, the effect of delay in carbonation initiation on the degree of carbonation and carbonation depth was investigated as well. Hence, the specimens were Pre-Cured for 1 day, 3 days, and 7 days followed by carbonation curing. The above mentioned methods were used for investigation. Using the DTA analysis it was concluded that CO2 was able to penetrate 5 to 10 mm deeper than the carbonation depth measured by the phenolphthalein method, irrespective of carbonation curing initiation.