More than 3 A Levels?

If your DC is very bright and can easily cope with four (and one is, as others have said, Further Maths or a language etc) then go for four and they might be more likely to get an offer from the very top universities. The offer itself will most likely be just for three grades though.
However if there's a chance studying four will risk 'diluting' the grades to a lower level then stick to three.
One of DS's friends came unstuck - had an offer of AAA but got AABB and wasn't accepted into his first choice (Durham).
However, another friend with a very similar profile didn't get an offer from Durham in the first place and thinks it was because he wasn't doing FM.

My DD is a high achiever also(9 A* and 2 9s at gcse )
She chose to do 3 because she needed high grades to get into her top uni choices. She had interviews at Oxbridge and has a conditional offer for a top RG uni.
So he doesn’t need to do it.

Pupils normally do no more than 3 at our school.

The main exception is those who do double maths, who end up with 4 (still 3 subjects: 2x maths plus 2 others) and very occasionally a good linguist, usually only if the extra language is one spoken at home - sometimes not even one the school teaches, but they agree to enter plausible candidates)

My daughter has just finished her first year in college and done Maths,further Maths, physics and Chemistry.
From what she has said Maths and Further Maths are very very different and equally as much work. There is more of a cross over with maths and physics than with the two maths subjects.
She is hoping to do Maths as a degree and we are currently doing the Uni visits and she will need both Maths and FM at most of them so it may depend what degree route he wants to go down. She got nine grade nines at GCSE and has coped quite easily doing the four although she has comtemplated dropping chemistry a couple of times to concentrate on trying to acheive 3 A stars. One last point that I have been told though that FM doesn't always count as a full A level for some UNI degrees so might be worthing checking.

Sorry, should have said the only time schools expected anyone to sit four was if you did M and FM, and like I say, not even always then. A mate of Ds's is doing M, FM, biology and computing but he is super bright (like, scored 99% in his GCSE maths mock)

Ds2 is in sixth form in Sept and no schools we looked at expect you to sit four a levels. Some start with four and drop one. Some do have FM as a fourth but more and more (including his final choice) do not, it's a lot of work and certainly counts as an A level. In fact it's a facilitating subject if you are fussed about that.

I agree with PP, why do four and risk poorer grades? A levels are tough, harder perhaps than they were when some pp sat them

I don't think Maths & Further Maths together have anything like the workload of, say, History and Biology.

A combination like Maths, Further Maths, Physics and Chemistry will be one of the easiest four A level combinations (easy in terms of workload).

Maybe Maths, Further Maths, Physics and Computer Science would be easier?

It’s important to appreciate as well that the system has changed. The new Linear A levels are less suited to doing 4 and in my experience the only ones doing 4 are either taking maths and FM or are taking a language as a native speaker.

At ds' s school everyone does 3 unless invited to do 4. They used to start everyone on 4 and drop 1 but that finished 2 years ago.

What is the earthly point of pushing kids to do 5 A levels when the universities offer only on 3? Currently deep in to open days and I've not seen a single university Entry Requirement that is more than 3 A levels.

I have a ds in Y12 and so all his friends (at both state and super-selective-often-cited-on-MN private schools) are coming to the end of the first year of A-levels. The only ones doing more than 3 are doing combinations your ds might fancy, OP, such as Maths/FM then two out of Biology, Physics, Chemistry. A couple are doing M/FM/Physics then Economics or Spanish or Government & Politics or Geography.

This is what Cambridge says for (random pick on my part) Physics:

*Number of A Levels
Our typical offers are based on students taking three A Levels together in Year 13, and most Cambridge applicants are studying three or four A Level subjects in Years 12 and 13. This is usually sufficient to show breadth of interests and ability to manage a range of differing academic tasks. We’d rather applicants develop broader and deeper knowledge of the subjects most relevant/closest to their chosen course than accumulate additional A Levels.

Applicants taking four subjects won't normally be at an advantage compared with those taking three, although competitive applicants for STEM courses often have Further Mathematics as a fourth subject.

For courses where A Level Mathematics is required by all Colleges – Computer Science, Economics, Engineering, physical sciences options in Natural Sciences – students taking A Level Mathematics in Year 12, and A Level Further Mathematics and only one other A Level in Year 13 will be considered.*

DD1 did 5 - very pushy 6th form college. She did well but incredible pressure. She advised her younger sibling to stick to 3 as that's all that a uni will need.

I suppose we can only comment on our own experience, and ours would be DD1 at super selective, started with 4, dropped one at AS, continued with three. I don't know anyone who did 4 or indeed 5.

DD2 selective, but choice is either 4 and drop one at AS, or 3 plus an EPQ. They are also encouraged to pursue other curricular subjects, which they choose to do to GCSE or just do for fun and extension of experience.

At DS's selective school most do 4 a levels.
DD was at a super selective school and many did 4 or 5.
I don't think it benefits university entrance but is a personal choice and as long as grades don't suffer can be done.

DS just taken A level maths, further maths, physics and economics. Didn’t find it a stretch because there is so much overlap, admittedly he is very bright. Plus economics is the only subject that is an essay subject so this combination worked really well and was very manageable. Although his uni offers have been made on three A levels the extra A level gives more UCAS points.
His school directive , same as Dds is to start with 4 and then if needed drop one before mocks in the final year.
Dds school have warned that in some instances where students take 4 then there is a possibility offers will be made on 4 but I haven’t come across any in DS year this year where that has been the case!

DD's school start everyone off on 4.
If you are struggling or not getting on with one, you have a chance to drop it.

My understanding is that universities only ever give 3 grade offers. So AAA is better than AABB. I may be wrong though.

I think the advice is to make sure that you get three high grades rather than four mediocre grades.

But there are some students who are capable of getting four (or more) high grades and want to do them.

Although university admissions will say that they only look for three I think there is anecdotal evidence to suggest you are more likely to get an offer from a top university if you offer four subjects or three plus an EPQ. And many private schools would consider that to be the norm.

I think a maths and FM combination is usually considered as one and a half A levels. But many state schools do not offer FM.

At my highly selective school (20 years ago, admittedly) the average was 4.5 A levels. And yes, if you do double maths most schools expect you to do 4. There’s also a lot of overlap between double maths and physics...and some with chemistry. So I think my 4 (plus AS French) was much less work than doing four essay subjects (this flipped 180 degrees at uni when labs kicked in!).

I reckon "it depends" is the answer! I went to a grammar and we all took 4, plus general studies. If he's bright and interested, he'll be fine.

Only thing I'd say is that for some courses Further Maths isn't actually counted as a separate A Level, or at least it wasn't when I was at school 15 years ago (e.g., a friend of mine did maths, F. Maths, Physics and Chem but was told by Cambridge, that that counted as three).