You should consider making a new will if you have married or entered into a civil partnership since making your old will, as this will generally automatically revoke it. That means that your will is invalid. It depends on the circumstances, but if you die without making a new one your estate will probably be distributed according to the intestacy rules.
You should review your will if there are births, deaths, marriages, name changes, bankruptcies, civil partnerships, divorces, ending of civil partnerships or relationship breakdowns, in your life or among your beneficiaries, or if an executor dies or is unable to act for any reason. You should also review it if your financial circumstances change significantly — for example, if your estate looks likely to go over the inheritance tax threshold of £325,000 for the first time or if changes in tax law are likely to have an impact — or if you or a beneficiary need to go into a nursing or care home.
In any event, you should review your will every few years to check that it still reflects your wishes and in case any changes are needed. For example, you may need to appoint a new executor if an executor named in your will has died.