Scores for each of the four parts are equally weighted. The overall band scores are calculated by taking the mean of the total of the scores of the four individual parts.
Overall band scores are reported to the nearest whole or half band. For the avoidance of doubt, the following rounding convention applies: if the average across the four skills ends in .25, it is rounded up to the next half band, and if it ends in .75, it is rounded up to the next whole band.
Thus, a candidate achieving 6.5 for Listening, 6.5 for Reading, 5.0 for Writing and 7.0 for Speaking would be awarded an overall band score of 6.5 (25 ÷ 4 = 6.25 = Band 6.5).
Similarly, a candidate achieving 4.0 for Listening, 3.5 for Reading, 4.0 for Writing and 4.0 for Speaking would be awarded an overall band score of 4.0 (15.5 ÷ 4 = 3.875 = Band 4.0).
However, a candidate achieving 6.5 for Listening, 6.5 for Reading, 5.5 for Writing and 6.0 for Speaking would be awarded band 6 (24.5 ÷ 4 = 6.125 = Band 6).
For more information on how IELTS test material is produced, download the IELTS Question Paper Production Process.