There is a standard payment.
Single and under 25 £344
Single and 25 or over £411.51
In a couple and you’re both under 25 £490.60 (for you both)
In a couple and either of you are 25 or over £596.58 (for you both)
Then you'll get help toward rent, not mortgage. If you're renting a house with more rooms than you need, you'll lose a percentage per room.
(My house is 3 bed HA and i lose %14 I believe)
You'll also get a set payment per child, up to 2 children.
For your first child £282.50 (born before 6 April 2017)
£237.08 (born on or after 6 April 2017)
For your second child and any other eligible children £237.08 per child
If you have a disabled or severely disabled child £128.89 or £402.41
If you need help with childcare costs up to 85% of your costs (up to £646.35 for one child and £1,108.04 for 2 or more children)
There's currently an uplift of £80 a month, but that ends soon.
Entitled too is good site.