What is the current nil-rate band and residence nil-rate band/what do they do?

The current nil-rate band is frozen at £325,000 until at least 2030. This means 
that on death, no IHT is paid on the first £325,000 of any estate. Anything above 
this value will then be subject to the 40% (or 36% in certain circumstances) IHT 
charge.

There is an additional Residence Nil-Rate Band of £175,000, also frozen until at 
least 2030, when a main residence property is included in an estate, and it is left 
to a direct dependant. If this is the case, then this is means that the value of the 
estate must surpass £500,000 before any IHT will be due.