Subscription line facilities, explained
A subscription line facility is a short-term loan to a private equity fund, secured by the fund's LP commitments. Instead of calling capital from LPs immediately when the fund wants to do a deal, the fund borrows from a bank, does the deal, and then either repays the loan from future exit proceeds or calls capital from LPs later to repay. Subscription lines, commonly called "sub lines" or "capital call facilities", became widespread in PE around 2010 and grew explosively in 2015-2022. They let PE firms report higher IRRs by delaying capital calls, which improves the time-weighted return calculation. They also simplify the operational experience for LPs. And they have become quietly controversial, because the IRR improvement they produce is mathematical, not fundamental, and can mask underlying deal-level performance.
That is the textbook answer. Here is what actually happens.
The mechanics
A PE fund has $5 billion of LP commitments. The fund wants to close on a $500m acquisition today.
In the traditional model, the fund would send a "capital call notice" to LPs, giving them 10-15 days to wire the money. LPs have to scramble cash, sell other investments if necessary, and fund the call.
With a sub line, the fund instead borrows $500m from a bank. The bank is secured by the fund's unfunded commitments (the LPs' legal obligation to fund when called). The fund uses the $500m to close the deal immediately.
Six months later (or eighteen months later, depending on the facility terms), the fund either:
- Calls capital from LPs and uses the called capital to repay the bank, or
- Repays the bank from proceeds of a portfolio company exit or sale
From the LPs' perspective, the capital call came 6-18 months later than it would have otherwise. From the fund's perspective, the deal closed immediately.
Why sub lines improve IRR
Here is where it gets interesting for the GP.
PE fund IRR (internal rate of return) is calculated based on the timing of cash flows in and out. When LPs fund later, the IRR benefits because the "clock" on their capital started later.
Consider a deal that exits in year 5 for a 2.5x return.
Without sub line: LP funds the deal in year 1. By year 5, they get back 2.5x over 4 years of holding period. IRR on that money is roughly 25.7%.
With sub line (LP funded in year 2.5): LP funds 18 months later. By year 5, the holding period is only 2.5 years for the LP, but the multiple is still 2.5x. IRR on that money is roughly 44.3%.
Same deal. Same multiple. Same operational performance. But the IRR looks dramatically better because the sub line shifted the capital call later.
This is the single biggest reason sub lines have become dominant. The mathematical effect on reported IRR is substantial, and IRR is the metric LPs and fundraising docs focus on. A fund that reports 22% IRR looks meaningfully better than one reporting 18%, even if the underlying deals are similar.
The cost
Sub lines are not free. The bank charges interest (typically SOFR/LIBOR + 1-2%), plus an unused facility fee. On a $1 billion sub line used at 50% average utilisation, the annual cost might be $25-40 million.
This cost is paid by the fund, which means ultimately by the LPs (the interest expense reduces the fund's returns to LPs).
So the sub line reduces nominal LP returns slightly while improving reported IRR dramatically. For the GP, this is a great trade: better fundraising optics in exchange for a small reduction in actual LP economics.
For the LP, it is a worse trade: they get lower absolute returns in exchange for higher IRR optics, which mostly benefits the GP's next fundraise.
How sub lines grew
Sub lines were uncommon before 2010. They grew rapidly in the low-rate era of 2015-2022 because interest costs were negligible.
By 2022, an estimated 80% of PE funds had sub line facilities. Utilisation rates varied: some funds used sub lines aggressively (keeping high balances for extended periods), others used them only for short-term bridging.
The secondary market for sub line exposure also developed. Specialist lenders (HSBC, SMBC, ING, Bank of America, JPMorgan in the US; various European banks) built large books of sub line exposure. Some private credit funds started participating.
The ILPA pushback
In 2020, the Institutional Limited Partners Association (ILPA) published guidance urging GPs to be transparent about their sub line usage and to report IRR both "gross" and "net of sub line" so LPs can see the underlying deal performance separately from the IRR enhancement.
This guidance was partially adopted. Many GPs now report both IRR measures. Others resist.
The practical effect has been that sophisticated LPs now routinely ask about sub line usage during due diligence and negotiate side letters restricting aggressive use. Smaller LPs often do not, which creates an information asymmetry.
The 2025/2026 picture
Higher interest rates have changed sub line economics materially.
In 2020, borrowing at 2% was cheap enough that sub lines made sense for almost any horizon. In 2025, borrowing at 7% is expensive enough that the arithmetic starts to erode.
Many funds have pulled back on sub line utilisation. Some have let their facilities expire. The consensus now is that sub lines are useful for short-term bridging (1-6 months) but expensive for long-term optics (12-18 months).
Regulatory scrutiny is increasing. The SEC's Private Fund Adviser Rules would have required more granular disclosure of sub line usage; the rules were partially vacated on appeal but the direction of travel is toward more transparency.
LP pressure continues. Large sophisticated LPs explicitly demand sub-line disclosure as part of due diligence and negotiate limits. Smaller LPs are catching up.
When sub lines are reasonable
Sub lines make sense for specific operational reasons.
Deal-timing flexibility. Deals close on compressed timelines. Capital calls to LPs take 10-15 days. Bridging with a sub line is operationally necessary.
LP operational simplicity. LPs get fewer, larger capital calls instead of many smaller ones. Easier to manage, less operational burden.
Ability to take down allocations. Sub lines let funds commit to deals in competitive processes without waiting for capital calls, which can be the difference between winning and losing deals.
These are legitimate uses. The question is whether the "optical IRR enhancement" use case has overrun the operational use case.
How to read a fund's sub line disclosure
When you see a PE fund discussion of sub line usage, the useful questions are:
How big is the sub line relative to committed capital? Facilities of 15-30% of committed capital are standard. Larger facilities mean more aggressive potential use.
What is the average utilisation? High utilisation (70%+) for extended periods indicates aggressive use. Low utilisation (under 30%) suggests bridge-use only.
How long is the typical bridge period? Six months or less is operational use. 12-18 months is optics use.
Does the fund report IRR net of sub line? If yes, the fund is being transparent. If no, treat reported IRR with caution.
Who are the lenders? Blue-chip banks with established sub line businesses are more stable. Less-specialised lenders may pull facilities in market stress.
The closing take
Sub line facilities are a classic example of a structural innovation that started as a sensible operational tool and evolved into an IRR-enhancement trick. The underlying capability (bridging capital calls to smooth deal execution) is valuable. The way it is used in practice (maximising reported IRR for fundraising) is less defensible.
The recent rate environment has changed the economics. Sub lines are no longer costless, so the cost-benefit calculus on aggressive usage has shifted. Expect continued retrenchment.
For LPs, the ask is transparency: net-of-sub-line IRR reporting, disclosure of utilisation, and thoughtful restrictions on facility size and tenor.
For the broader picture of how PE firms generate reported returns, see what is private equity and the LBO model. For other tools PE firms use to manage fund-level cash flow and LP optics, see NAV lending and continuation funds, and the rest of the toolkit.
