Bihar has a population growth rate of 18.24% during 2011-2021. In 1910 Population of Bihar was 2.1 Crore & in the Year 2021, it’s estimated to reach 12.30 Crore, an increase of almost 10 Crore. Let’s look at decade population & percentage change from the Year 1910 to 2021
| Census Year | Population | Absolute Change | Percentage Change |
| 1901 | 21,243,632 | – | – |
| 1911 | 21,567,159 | +323,527 | +1.52 |
| 1921 | 21,358,905 | -208,254 | -0.97 |
| 1931 | 23,438,371 | +2,079,466 | +9.74 |
| 1941 | 26,302,771 | +2,864,400 | +12.22 |
| 1951 | 29,085,017 | +2,782,246 | +10.58 |
| 1961 | 34,840,968 | +5,755,951 | +19.79 |
| 1971 | 42,126,236 | +7,285,268 | +20.91 |
| 1981 | 52,302,665 | +10,176,429 | +24.16 |
| 1991 | 64,530,554 | +12,227,889 | +23.38 |
| 2001 | 82,998,509 | +18,467,955 | +28.62 |
| 2011 | 104,099,452 | +21,100,943 | +25.42 |
| 2021 (Estimated) | 123,083,000 | +18,983,548 | +18.24 |
Source: Census 2011 & Census Population Projection report 2021-36