Gap year applying to Cambridge Maths with 4 A Levels

I am in year 13 and doing maths , further maths , bio and chem. I’m going to take a gap year and apply to Cambridge afterwards for bionatsci. I’m struggling with further maths and chemistry but want to keep further maths. I’m thinking of dropping chemistry then going it in the gap year , is this acceptable for Cambridge / will it decrease my chances of acceptance if I do an a level in a gap year??

If the A level in the gap year is a requirement for the course, it will disadvantage you to the point of not being competitive.
If the A level take during the gap year is not required, then it will probably largely be ignored and your offer will be based on your existing grades.
No-one knows how an individual College and admissions tutor will approach the situation where you have marginal grades in year 13, and a predicted grade in the gap year, the tight be better. However, it's a big risk and probably would not play in your favour.
Bottom line, you're playing a poor strategy. You should have applied this year, with 4 or 3 A levels, for deferred entry. If you got an offer, chances are it would be based on 3 anyway. If you didn't get an offer, you'd have had a second bite in your gap year.

I am applying to Cambridge Natural sciences from a competitive independent school where the majority of people take 4 a levels. Everyone in the past 5 years who has gotten into the course from my school has taken 4 a levels. I know Cambridge say 4 doesnt have an advantage over 3 but is this actually true? As im pretty sure they expect people to do 4 if most in their school does 4 right? My guidance counsellor showed my the data over the last 5 years and from my school only oeople with 4 a* got in. Therefore as Cambridge compare you against people from your school, am i at a disadvantage with 3?

Haven't you asked this about 3 times in the past month?!
3 A levels are fine - assuming you've checked the Natsci admissions page and your subjects contain the necessary ones. If the "majority" of pupils from your school take 4, then obviously the stats are going to show that most successful applicants from your school have 4 - it's a self-fulfilling prophecy!
Better to have 3 strong A levels and some really good super-curricular activities that demonstrate your passion for the subject you want to study, rather than push yourself on 4 A levels and risk dropping a grade if one of those subjects is a weaker one for you.

Sorry, last question. Would you say 3a* is not as good as 3a* + a. And if that’s a no, then would 3a* be better than 2a* and 2a ?

Yes, I think 3A* + A is better than just 3A*s. It shows enthusiasm for studying and an ability to take a high workload, which is extremely important at a high-achieving university like Cambridge. But, I think 3A* is better than 2A* + 2A. (This sort of looks like your grades are slipping because you're taking too many subjects.)
Can I ask which A levels you're doing? And which natural sciences are you applying to? For example, for the physics natural sciences, Further Maths is a big one. And if your school offers Further Maths but you're not taking it, then this suggests that either you're not interested enough in the subject or that you can't take the workload, which would disadvantage your application. However, if you're doing e.g. Maths, Further Maths, Phsyics, and the fourth subject is not super relevant to nat sci like economics or something, then I would just focus on getting 3A*, and the perfect grades will help your application.

Thank you very much for the reply. Can i ask a question though - basically why would i be disadvantaged with doing one in my gap year and applying with a predicted grade?? Surely the vast majority of applicants apply with a predicted grade for the course. Is the fact that i am doing the a level over three years the reason why i would be disadvantaged?

Because 'scoring' A levels, which is only 3, need to be done in tow years. That is how you demonstrate you have the capacity to work at the pace required of the course. By taking a 'scoring' A level over 3 years, or in a 3rd year, you take the pressure off yourself. That's not useful for Cambridge.

Ah ok, thanks. But surely i still show i can handle pressure if i do 3 now and one in the gap, or will that disadvantage me as well? I come from a competitive independent school where most do 4, if i then choose to do 3, will that be a disadvantage ?

I am in year 13 and doing maths , further maths , bio and chem. I’m going to take a gap year and apply to Cambridge afterwards for bionatsci. I’m struggling with further maths and chemistry but want to keep further maths. I’m thinking of dropping chemistry then going it in the gap year , is this acceptable for Cambridge / will it decrease my chances of acceptance if I do an a level in a gap year??

How many ways do you need this explaining to you? I've already answered this. Your strategy is weak. You should have applied this year, with 3 strong A levels, only doing a 4th if it wasn't going to affect the grades of the first 3.
As explained multiple times, your attempts to reduce the pressure and get better grades does weaken your application. However, that doesn't mean it will definitely fail, so stop making more threads on the same subject, and put your time to better use improving your A level grades.

I do maths, further maths, biology and chemistry. If i apply for natural sciences i will apply for bionatsci

I am applying to Cambridge Natural sciences from a competitive independent school where the majority of people take 4 a levels. Everyone in the past 5 years who has gotten into the course from my school has taken 4 a levels. I know Cambridge say 4 doesnt have an advantage over 3 but is this actually true? As im pretty sure they expect people to do 4 if most in their school does 4 right? My guidance counsellor showed my the data over the last 5 years and from my school only oeople with 4 a* got in. Therefore as Cambridge compare you against people from your school, am i at a disadvantage with 3?