Defence
CDS preparation
Combined Defence Services — IMA, INA, AFA and OTA entry for graduates.
24 free guides·Conducted by Union Public Service CommissionOfficial website
About the CDS exam
The Combined Defence Services exam is UPSC’s route for graduates into four officer academies: the Indian Military Academy, the Indian Naval Academy, the Air Force Academy and the Officers Training Academy, Chennai. It is held twice a year, and the only limit on attempts is the age window. Recent notifications open only the OTA to women. That rule is being challenged in court, so check the notification for your cycle.
IMA, INA and AFA candidates sit three objective papers of 100 marks each: English, General Knowledge and Elementary Mathematics. OTA candidates sit only English and GK. Every wrong answer costs a third of the question’s marks. If you clear the written cut-off, you go to a five-day Services Selection Board, which carries as many marks as the written exam. The final merit is out of 600 for IMA, INA and AFA and out of 400 for OTA. A strong SSB can overturn a written lead.
The Start here guides cover the pattern, eligibility, what each academy offers, the syllabus, a six-month plan, negative marking, merit and the SSB. Then go subject by subject. The maths is Class 10 level but the clock is tight. English and GK reward a little work every day. Begin SSB and fitness work alongside the books, because the gap between the written result and the board is short.
| Papers | English, General Knowledge, Elementary Mathematics: 100 marks and 2 hours each |
|---|---|
| OTA candidates | English and GK only (200 marks) |
| Negative marking | ⅓ of the question’s marks; multiple options marked counts as wrong |
| SSB | 300 marks (OTA 200) |
| Final merit | 600 for IMA, INA and AFA; 400 for OTA |
Patterns change. Confirm details in the latest notification on the official website.
Start here
New to CDS? Read these first, in this order.
- 1The CDS exam pattern explainedThree papers for IMA, the Naval Academy and the Air Force Academy; two papers for OTA; negative marking in all; and an SSB that carries as much weight as the written exam. The CDS pattern explained clearly.
- 2CDS eligibility: academy-wise age and educationEach CDS academy has its own age window and degree requirement, with an engineering degree for the Naval Academy and physics and maths for the Air Force Academy. The rules explained academy by academy, with worked age checks and a checklist.
- 3IMA, INA, AFA and OTA: what each academy offersFour academies, three services, two kinds of commission. Where each CDS academy is, roughly how long training lasts, what rank and commission it leads to, and how to order your preferences.
- 4The CDS syllabus, analysedElementary maths at Class 10 level, an English paper that tests usage rather than literature, and a very broad General Knowledge paper. The syllabus paper by paper, what it really asks, how to set priorities, and a tracker.
- 5A six-month CDS planSix months is enough to prepare seriously for CDS. A month-by-month plan for maths, GK and English, a daily and weekly structure, SSB and fitness work alongside, checkpoints, and how to adjust when you fall behind.
- 6Negative marking and accuracy in CDSIn CDS, a wrong answer costs one-third of the question's marks. With 120 questions in English and GK and 100 in maths, careless errors add up fast. The arithmetic of guessing, worked examples, and habits that protect your score.
- 7How CDS merit and cut-offs workClearing the written exam depends on academy-wise cut-offs; final selection depends on written plus SSB marks, medical fitness and your preferences. How the pieces fit together, with worked examples, and what it means for preparation.
Subject by subject
Strategy
Guides on the pattern, academy-wise eligibility, OTA versus IMA, study plans, negative marking, merit and the OTA route for women. Age windows differ by academy, and the INA window now matches the IMA’s, so go by the current notification rather than older lists.
- The CDS exam pattern explained
- CDS eligibility: academy-wise age and education
- IMA, INA, AFA and OTA: what each academy offers
Mathematics
Elementary Mathematics is 100 questions in two hours at about Class 10 level. IMA, INA and AFA candidates take it; OTA-only candidates don’t. It covers arithmetic, algebra, trigonometry, geometry, mensuration and statistics, and speed and short methods decide the score.
All 10 Mathematics guides