IHTM26040 | Calculating the chargeable estate: calculation where there are no specific gifts
From HM Revenue & Customs · Inheritance Tax Manual
If there are no specific gifts, the residue (IHTM26003) is the whole estate. The part or proportion of the estate taken by the exempt beneficiaries or bodies will be exempt. The rest is chargeable.
Example
Under his will Trevor gives his whole estate in following proportions
The three-quarters given to the spouse and charity are exempt. The remaining one-quarter is chargeable.