Cat B has two parts. Both need to be passed.
Part 1: Current gross annual income at the level of at-least 18,600
Part 2: Total at-least 18,600 made in 12 months prior to the application date. We have made about 19k, so my question is regarding part 1.
I have a general idea about the calculation and formula used by the caseworker. Please check and let me know if you see anything wrong.

I have two current jobs. Both minimum wage jobs.
Job 1: Working for the last 13 months. Paid fortnightly. So far I have 29 payslips from Job 1.
Job 2: Just started, in her second week. Paid weekly.
So, we will use two current jobs to show that I have at least 18,600 current gross salaries to pass part 1.
Excerpt taken from Appendix FM SE
(f) For the purpose of paragraph 13(b)(i), “the gross annual salary from employment as it was at the date of application” of a person in non-salaried employment at the date of application shall be considered to be the annual equivalent of:
1. (aa) the person’s gross income from non-salaried employment in the period immediately prior to the date of application, where the employment has been held for a period of no more than one month at the date of application; or
2. (bb) the person’s average gross monthly income from non-salaried employment, where the employment has been held for a period of more than one month at the date of application.
so from the above excerpt Job 1 falls under 2(bb) and job 2 falls under 1(aa).
Job 1 income:
(Total income/Number of payslips) * 26 (because fortnightly payslips)
(10109.26/29) * 26 = 9063.47
Job 1 Gross monthly income = 9063/12 = 755.28
Job 2 income:
I am estimating how many days I will be working based on rota and unpaid bank holidays in coming weeks.
Week 1: 12th Dec, 13th Dec=> 21 Hours
Week 2: 15 Dec, 16 Dec, 17 Dec=> 31.5 Hours
Week 3: 22 Dec, 23 Dec=> 21 Hours
Week 4: 30 Dec, 31 Dec, 2 Jan => 31.5
Total 104 hours in 4 weeks' weekly payslip.
Total income in 4 weeks => 8.21 * 104 = 853.84
Average weekly income => 853.84/4 = 213.46
Gross annual income from
job 2 => 213.46*52 (because weekly payslip) = 11,099.92
Gross monthly income from job 2 => 11,099.92/12 = 924.99
Let's add gross monthly income from both jobs
Job 1 + job 2 = 755.28 + 924.99
= 1680.27
Total current gross annual income 1680.27 * 12 = 20,163.24
So this is my best-case scenario. Please check if this calculation and method is correct or not. I will adjust my work hours based on your advice. For job 1 I am currently working fewer hours past 2 weeks to focus on Job 2. Job 1 income will be counted as an average combining total income, I am assuming it won't affect much. Please advice.
[ I am sponsoring my husband who is currently in the UK on tier 2 visa, lost his job ]