As is becoming traditional, our member-on-sabbatical, Gayot Fow, wrote an excellent answer on his blog. Given the explicit permission at the foot of the original article I quote most of it here. Everything below the line is his.
By way of background, large portions of the UK rules are left ambiguous by design and intent, and the computation of monthly income falls into that category. Unlike other visa applications, say those in the Points-Based System, there are no published guidelines that specify a methodology. It is therefore down to the applicant to produce a monthly income figure that is (1) reasonably calculated; (2) gained legally; (3) absolutely and fundamentally provable and supported by high-quality evidence. People will often fail on item (3), but that’s a topic for a future article.
His questions (and my answers) are…
Calculate the average of the last 6 months, use that amount and mention that in the cover letter?
This is fine as long as the 3 conditions above are met. Evidence can always be improved if supported by a recent tax return so consider adding this to your evidence.
I wouldn’t put that kind of detail in your cover letter because it will unnecessarily clutter things. If you feel the number needs an explanation, consider adding an addendum page to your cover letter that details the steps you took.
How should I handle my pay check with the yearly bonus? Should I include that in the average calculations?
Hmmm… what does ‘yearly’ mean to you? It means something like ‘annual’, right? Those terms do not fall into the meaning of ‘monthly’ because annual bonuses are not part of your monthly income. That’s why they call it an ‘annual bonus’ 🙂
However, lots of people feel compelled to aggregate their annual bonus because it makes the monthly figure look more prosperous. This is a case where ambiguity works in your favour and so it’s fine to pro-rate your annual bonus into a monthly amount. As long as the 3 conditions listed above are met, they will accept your calculation without a problem.
Or is there any other way to do represent this?
What’s a ‘month’? What’s ‘income’? What if you get alimony or child support? What if you collect dividends and live off those? What if you are a professional gambler? What if part of your salary is garnished by a collection agency? What if you are making deductions to a retirement or benefits scheme? There are too many different angles to consider and so UKVI makes it all ambiguous (many times this will work in your favour). And yes, there are innumerable ways to compute the monthly income figure. There is no single ‘correct’ way to do it. The 3 items listed above include that the result must be reasonable and supported by high-quality evidence.
There’s not much more that can be said about it. Throwing this sort of question into an internet forum or TSE is essentially an opinion-poll where you will get lots of different answers and all of them will be partially correct. Examine your evidence, compute the number, enter it on the form, and if you think your number is not immediately obvious, then add an addendum page.