With reference to the second bullet point of the following visa refusal notice, my question is what is the ideal percentage gap between the opening and closing balance of a 6-month bank statement when it comes to applying for a Standard Visitor visa for the UK?
The problem is not so much the increase of the balance, either in absolute or relative terms. If an applicant with a reasonable income but spending a lot of it each month had £1000 in their account and 6 months later they had £3000, then it would amount to a +200% increase, but that could just be the applicant saving up for their next holidays, after which they would just go back down to £1000, rinse and repeat. So there's no "ideal percentage" or anything like that.
A first issue is the discrepancy between your statements on your income and expenditure and your actual bank balance. You basically state that you have 5000 QAR left each month (10K income - 5K expenditure), but in less than 6 months your balance increased by 43000 QAR. There's more than 10K extra. No idea where the discrepancy comes from, but unless you can justify it (e.g. end of year bonus), it may look like funds parking.
If you received money from someone else for instance, that makes the situation complicated, because the officer reviewing the application cannot determine if that money is actually yours to spend or if it's just a loan.
Then, they find it weird that you manage to save up that much during those 6 months, but don't have a lot more saved up from the previous 10 years you have been working. That seems like a terrible excuse, as there could be many reasons for not having more (as above, you could save up the whole year to then take a nice big holiday every year, or there could have been a variety of life events that made you spend a good chunk of your savings), but again, that seems "off" to them.
I would add (they don't mention it), that it seems slightly unusual for someone to keep that much on a current account. Most people would move a good chunk of that to savings accounts or other forms of investment. If you have any of those, you should have provided statements for them as well, that would have given a better picture of your full financial situation.
It's also relatively unusual for people to manage to save up that much of their income every month. Most people have a hard time saving even a fraction of that, so half of their salary... If that's really the case, good for you! But that's probably unusual enough that it makes them raise an eyebrow.
All in all, they're in "there's something off" mode, and they think that you provided incorrect or incomplete information, and they doubt the whole thing. Of course if any of the information or documentation you provided is false or fake, they're quite justified in their response.
Don't try to "massage" things to make them look like what you think they want. But make sure you give them a full, accurate picture of the situation, where everything is completely justified.
