The short answer is everything you own at the time of your death. This includes any assets which you own jointly (as well as those you own individually).
Examples of assets you might own include:
Life policies and pension policies only form part of your estate if a payment will be made to your estate when you die (as opposed to someone you have nominated to receive the payment such as your spouse, civil partner or children).
All property belonging to you will need to be valued in order to begin probate. The valuation needs to be as at the date of your death. Probate refers to the process of proving that your will is valid, and then the right to deal with your assets and estate. For more information on probate, please see our page Probate.
However, it is also worth estimating the value of your estate before you begin making your will. Doing so may clarify the nature of your estate, i.e. exactly what it is made up of, and the proportion of your estate that is represented by each of those assets. This, in turn, may help you when considering how you would like those assets to be distributed, and to whom.
In addition, valuing your estate will give you an idea as to how much inheritance tax may be due on it. So when you estimate the value of your estate, it is important to be as precise as possible.
The value of your estate is the total value of your assets minus the total value of any liabilities you may have. Liabilities refer to what you owe, such as an outstanding mortgage, overdraft, loans, credit card bills and other debts.
We've prepared a handy sheet that you can print out to help you with the sorts of things that you should include. It isn't comprehensive - we can't know everything that's in your estate - but hopefully it will jog your memory and has spaces for you to tot up as you go along. Just click this link: Estate valuation.