A Money Bill is defined in Section 1(2) of the Parliament Act 1911. It is a public bill which in the opinion of the Speaker of the House of Commons contains only provisions dealing with all or any of the following:

• the imposition, repeal, remission, alteration, or regulation of taxation;

• the imposition for the payment of debt or other financial purposes of charges on the Consolidated Fund or the National Loans Fund, or on money provided by Parliament or the variation or repeal of any such charges;

• Supply;

• the appropriation, receipt, custody, issue or audit of accounts of public money;

• the raising or guarantee of any loan or the repayment thereof;

• subordinate matters incidental to those subjects or any of them.

For a bill to be certified by the Speaker as a Money Bill, it must have the sole purpose of creating or extending the scope of a charge on public expenditure.

Finance Bills may be certified as Money Bills but not always, because they sometimes include provisions dealing with matters other than those listed above.

The Speaker is advised by officials about the certification of bills as Money Bills. (On a few rare occasions, certification has been done by the Deputy Speaker if the Speaker was unavailable.) Section 1(2) of the 1911 Parliament Act also imposes a ‘duty’ on the Speaker to consult, if practicable, two senior members of the Panel of Chairs.

The Speaker only considers certification when the bill in question has reached the final form in which it will leave the House of Commons. This is because the inclusion of an amendment could have a significant bearing on the certification decision. When MPs have attempted to assess whether an amendment is likely to prevent a bill being certified as a Money Bill, at the bill's committee or report stage, then the committee chair or the Speaker has always declined to give an opinion.

According to Erskine May, once a bill is certified as a Money Bill the Speaker’s decision is "conclusive for all purposes and may not be questioned in a court of law".

Under the terms of the 1911 Parliament Act, a Money Bill can be presented for Royal Assent with or without the agreement of the House of Lords one month after it was sent to the Upper House (providing that the Bill was sent to the Lords at least one month before the end of the parliamentary session). (In contrast, all other public bills passed by the House of Commons may be delayed by the Lords for a minimum period of 13 months, under other provisions in the 1911 Act.)

The House of Lords is not debarred from amending a Money Bill, provided that the amendments are passed within one month, but there is no obligation on the Commons to consider the Lords amendments. In practice, therefore, a Money Bill is rarely considered in committee by the Lords; the legislative stages on the bill are usually (although not always) treated as a formality.