One of the most-missed easy marks in 11+ maths. 4+6×2 is 16, not 20 — and papers test exactly that reflex several times. BIDMAS (also written BODMAS) is the rule that fixes the order you tackle a calculation, and once a child trusts it, these become some of the quickest, most reliable marks on the whole paper. This guide teaches the method step by step, shows the traps that lose marks, and links every skill to a free downloadable worksheet and a timed on-site mini-mock on Quest Arena.
What BIDMAS actually stands for
BIDMAS is a memory hook for the order of operations. Each letter tells you what to deal with first, working left to right when operations are equal:
- B — Brackets: do anything inside ( ) first.
- I — Indices (powers and roots), e.g. 3² or √16. BODMAS calls this "Orders".
- D and M — Division and Multiplication, ranked equally, done left to right.
- A and S — Addition and Subtraction, ranked equally, done left to right.
The single biggest thing to teach: division and multiplication share a rank, and so do addition and subtraction. You do not do all multiplication before all division — you sweep left to right through that pair. Same for add and subtract. This is where careful pupils still slip.
A fully worked example, step by step
Take 4 + 6 × 2. A child rushing left to right gets 4 + 6 = 10, then 10 × 2 = 20. Wrong. BIDMAS says multiplication outranks addition:
- No brackets, no indices, so look for × and ÷ first.
- 6 × 2 = 12.
- Now the addition: 4 + 12 = 16.
Now a harder Year 6 version: 20 − (3 + 2)² ÷ 5 × 2.
- Brackets first: (3 + 2) = 5, giving 20 − 5² ÷ 5 × 2.
- Indices: 5² = 25, giving 20 − 25 ÷ 5 × 2.
- Division and multiplication, left to right: 25 ÷ 5 = 5, then 5 × 2 = 10, giving 20 − 10.
- Subtraction last: 20 − 10 = 10.
Notice we did the ÷ before the × only because it came first reading left to right — not because D beats M.
Common mistakes and 11+ exam traps
These are the exact ways children drop the mark on a real paper. Warn your child about each one:
- Left-to-right blindly: ignoring that × and ÷ jump the queue ahead of + and −.
- Treating M before D (or A before S): forgetting equal-rank pairs are worked left to right.
- Missing hidden brackets: a fraction bar like (8 + 4) ÷ 2 acts as a bracket over the whole top line.
- Indices errors: reading 3² as 3 × 2 = 6 instead of 3 × 3 = 9.
- Negatives across zero: 5 − 8 + 2 is worked left to right as (5 − 8) + 2 = −1, not 5 − (8 + 2).
- Choosing the "obvious" wrong option: GL multiple-choice answers deliberately include the number you get from doing it left to right, so the trap is pre-baked into the answer sheet.
How BIDMAS appears in a real GL 11+ paper
GL Assessment now dominates most UK regions after CEM's separate 11+ tests were phased out around 2022–2023, and its maths papers are typically 50 questions in 50 minutes — about a minute per question — multiple-choice with answers A–E marked on a separate OMR sheet, no calculator. BIDMAS shows up as short single-line calculations, and also hidden inside worded and algebra questions where a child must evaluate an expression correctly. Because the wrong left-to-right answer is usually offered as one of the A–E options, a pupil who guesses the order will confidently pick the trap. Getting the routine right converts these into fast, dependable marks — and topic mastery is what lifts a raw score into a stronger Standard Age Score (SAS), which runs roughly 69–141 with 100 as average and many grammar schools looking for around 111+. In CSSE (Essex) and some independent papers you may also meet these inside free-response working, where you must show the ordered steps rather than just tick a box.
Difficulty progression: Year 5 vs Year 6
Build the skill in stages so it never feels like a cliff:
- Year 4/5 (easier): two operations, no indices, e.g. 3 + 4 × 5 or 12 − 6 ÷ 2. Just embed "× and ÷ before + and −".
- Year 5 (secure): add brackets and left-to-right pairs, e.g. (7 + 3) × 4 − 5.
- Year 6 (exam level): brackets, indices, and mixed division/multiplication in one line, e.g. 2 × (6 + 3²) ÷ 3 − 4, plus BIDMAS folded into algebra substitution.
How to use the free worksheets
Our free worksheet library grades every topic across four tiers — Foundation, Developing, Secure and Greater Depth — so a child can enter at their level and climb.
- Diagnose: one Secure-tier sheet, unaided. Score under 70%? Drop a tier. Over 90%? Climb one.
- Little and often: 15–20 minutes daily beats a weekend marathon — retention lives in the gaps between sessions.
- Review errors out loud: the child explains what went wrong; you resist explaining first. Self-diagnosis sticks.
- Fold into mocks: once a topic hits Greater Depth, let full timed mock papers keep it warm rather than more isolated drilling.
Every BIDMAS worksheet — with answer keys and OMR sheets — is free in our worksheet library under the Maths tab, and you can drill related skills like GL-style papers and the wider revision hub. Nothing sits behind a card or email wall.
Frequently asked questions
Is a calculator allowed in the 11+?
No. GL 11+ maths is a non-calculator paper, so BIDMAS must be done by hand and mentally. That is exactly why practising the ordered steps until they are automatic pays off under time pressure.
What is the difference between BIDMAS and BODMAS?
They are the same rule. BIDMAS uses "Indices" and BODMAS uses "Orders" for the same thing (powers and roots). Whichever your child's school uses, the order of operations is identical.
How much time should each question take?
In a GL paper of roughly 50 questions in 50 minutes, that is about one minute per question. Straightforward BIDMAS lines should take well under that, banking time for harder worded problems later. See our 11+ process guide and key dates to plan a realistic timeline.