So
Standard allowance - £617.60
First child - £333.33 (assuming born before 6/4/17. £287.92 if born after)
2nd child - £287.92
Rent - £440
Total = £1,678.85
Earnings minus work allowance
£2500 - £404 = £2096
Earnings deduction
£2096 x 0.55 = £1,152.80
Total - earnings deductions = total UC
£1,678.85 - £1,152.80 = £526.05
Savings deduction on the £4k over £6k.
£4.35 on every £250 or part of £250.
16 x £4.35 = £69.60
Total UC - savings deduction = total UC received
£526.05 - £69.60 = £456.45
More if you have childcare costs, have disabled DC, are a carer.
Applying mid month would be best.
If you and DH are paid 4 weekly then one, possibly 2 if your wages aren’t aligned, assessment period will have 2 pay days which would mean you wouldn’t receive any UC that month.