Pension funds hold portfolios that often look conservative and sometimes look odd. The shape is determined by the payments they have promised and when those payments fall due.
The liability comes first
A pension fund's starting point is a schedule of future payments stretching decades ahead, estimated from membership records and assumptions about longevity.
Assets are then selected to meet that schedule rather than to maximise return in isolation. The relevant risk is failing to pay, not underperforming an index.
This reverses the usual framing. The portfolio is built backwards from an obligation, which is why it can look unlike a portfolio built for growth alone.
Matching cash flows reduces the real risk
Long-dated government bonds are held heavily because their payment dates can be aligned with the years when benefits fall due.
When assets and liabilities move together in response to interest rates, the funding position is more stable even if the headline asset value fluctuates.
A fund holding only growth assets would see its funding level swing sharply with rates, because the value of its obligations moves while its assets do not follow.
Maturity of the scheme changes the mix
A young scheme with decades before major payouts can tolerate volatility, since it has time for values to recover before cash is needed.
A closed scheme paying out more than it receives has no such tolerance, because assets must be sold on a schedule regardless of market conditions.
Portfolios therefore de-risk as schemes mature, shifting from growth assets toward matching assets in a progression that is planned rather than reactive.
Illiquid assets fit an unusual balance sheet
Pension funds can hold assets that cannot be sold quickly, such as infrastructure and property, because their payment obligations are known far in advance.
That predictability is rare among investors, and it is the reason such funds appear as long-term owners of assets requiring patient capital.
The limit is set by how much liquidity the scheme needs for near-term payments and for collateral obligations, which constrains the share regardless of appetite.
Regulation and accounting shape behaviour directly
Funding rules require schemes to measure their position on a prescribed basis and to agree recovery plans with sponsors when a deficit appears.
Because the measurement basis affects the reported deficit, changes to it can alter investment behaviour across an entire market without any change in the underlying obligations.
The specifics vary considerably by jurisdiction and are revised periodically, so structures common in one country may be unavailable or discouraged in another.