The smallest dollar or share quantity that an investor can purchase when investing in a specific security or fund. Most often seen in relation to mutual funds, minimum investments are also found consistently in fixed-income securities hedge funds, collateralized mortgage obligations (CMO) and limited partnerships (LP) where $1,000 units is typically the smallest cut allowed.

Minimum investment amounts for mutual funds can stretch anywhere from $0 all the way to $1 million or more for institutional share classes. Hedge fund minimum investments can be even larger, as can some LPs and unit investment trusts. For retail investors, there remains a large selection of funds that have modest minimum investments of a few hundred dollars.

A big factor for a fund manager in determining a minimum investment size is the strategy and liquidity demands of the fund itself. By setting a high minimum investment, fund managers can effectively weed out short-term investors and regulate cash inflows to the fund, which can be helpful for day-to-day management of the assets.