Most Nigerian universities and polytechnics grade coursework on either a 5-point or 4-point scale. Before you can calculate your CGPA, you need to know which scale your institution uses — this is usually stated in your student handbook, and it changes the grade points attached to each letter grade.
On the common 5-point scale: A = 5 points, B = 4 points, C = 3 points, D = 2 points, E = 1 point, F = 0 points. On the 4-point scale, A = 4.0, B = 3.0 (or 3.5 for B+), C = 2.0, D = 1.0, F = 0.0. Always confirm your institution's exact breakdown before relying on any calculator, including this app's.
Step 1: For each course, multiply the grade point by the course's credit unit to get the "quality points" for that course. A course worth 3 units with a B (4 points) gives you 12 quality points.
Step 2: Add up the quality points for every course you took in the semester. Separately, add up the credit units for every course that semester.
Step 3: Divide total quality points by total credit units. That result is your GPA for that semester.
Step 4: To get your CGPA, repeat the process across every semester you've completed — sum all quality points across all semesters, sum all credit units across all semesters, and divide. CGPA is cumulative, not an average of your semester GPAs, so a semester with more credit units carries more weight.
Worked example (5-point scale): Semester 1 — 18 total units, 72 quality points → GPA = 4.00. Semester 2 — 20 total units, 76 quality points → GPA = 3.80. CGPA after two semesters = (72 + 76) / (18 + 20) = 148 / 38 = 3.89, not the simple average of 4.00 and 3.80.
A common mistake is averaging semester GPAs directly instead of recalculating from total quality points and total units — this gives a wrong CGPA whenever your credit load differs between semesters.