This page is more technical than the other pages. Its purpose is not to restate Benchmark theory in general, but to show where the traditional formulas stop functioning as one coherent year-by-year funding model, and why Reserve Sense uses a different implementation.

On this page, Legacy Method means the commonly used CRFR / FRFA / FRFR / ARFA / Reserve Requirements framework associated with the Functional Reserve Fund Study standard, typically applied with flat nominal ARFA contributions. Other variants exist, but this is the version addressed here because it is the version most commonly used in practice.

The Legacy Method has been the industry standard for many years. It was a meaningful step forward over simpler straight-line approaches and gave practitioners a workable way to incorporate future costs and investment income using the tools commonly available at the time.

Many practitioners learned and applied these formulas in good faith. The issue addressed here is not practitioner competence. It is whether the formulas themselves work coherently as one funding model.

This matters because the Legacy Method is not merely old-fashioned or approximate. In its commonly used form, it is mathematically inconsistent as a year-by-year funding model. Its formulas do not resolve into one coherent sequence of balances, contributions, interest, and expenditures.

The Reserve Sense Benchmark Method does not change the goal of Benchmark funding; it corrects the implementation.

The traditional sequence

In its usual form, the Legacy Method follows this sequence:

1. Estimate the component's Current Replacement Cost (CRC).
2. Project that forward with construction inflation to a Future Replacement Cost (FRC).
3. Calculate the Current Reserve Fund Requirement (CRFR).
4. Project that forward with interest to a Future Reserve Fund Accumulation (FRFA).
5. Define the remaining future shortfall as the Future Reserve Fund Requirement (FRFR).
6. Calculate an Annual Reserve Fund Assessment (ARFA) to fund that shortfall.
7. In later years, project future Reserve Requirements (RR).

Taken step by step, that sequence can sound like one complete method. But it is not one coherent cash-flow model.

Why CRFR is the starting problem

The first two steps, CRC and FRC, describe ordinary cost projection. They estimate today's cost then project it forward to the replacement year. The trouble begins at Step 3, when CRFR is introduced as the reserve fund balance target.

From that point on, the method is no longer just projecting future cost. It is trying to define what the fund should already contain, how that amount should grow, and what contributions should be made along the way.

That is where the internal contradictions begin.

CRFR links to a moving target

The Legacy Method begins with this formula:

$$CRFR=CRC\cdot \frac{EA}{LS}$$

where:

• CRC = Current Replacement Cost
• EA = Effective Age
• LS = Lifespan

That sets the target balance as a fraction of cost based on age consumed. In shape, that is a straight-line depreciation formula applied to a moving target.

In a sinking-fund framework, the analogous target would be based on a fixed future cost: namely, FCR. The Legacy Method instead applies the age fraction to CRC, which changes over time.

That makes the result look less obviously straight-line, but it does not solve the underlying problem. It turns a depreciation-style allocation into a moving target.

Using CRC brings construction inflation into the result and creates some appearance of time value, but not through one consistent cash-flow structure.

The later ARFA step then tries to add sinking-fund annuity logic on top of that moving target.

So the problem is not just that CRFR has an unstable starting point. It is that the Legacy Method combines two different frameworks:

• a moving-target straight-line balance formula, and
• a sinking-fund-annuity-style contribution formula.

As we will see, those do not naturally resolve into one coherent Benchmark model.

CRFR has no stable timing meaning

The next problem is timing.

A balance must belong to a specific moment in time. Is CRFR:

• an opening balance?
• a closing balance?
• a balance before an expenditure?
• a balance after an expenditure?

The Legacy Method never gives one stable answer.

Here is the same fitness equipment example used elsewhere in these pages, with a Future Replacement Cost of $10,000 and a construction inflation rate of 3.5%.

	Year 0	Year 1	Year 2	Year 3	Year 4	Year 5	Year 6	Year 7	Year 8	Year 9	Year 10
CRFR	$0	$734	$1,519	$2,358	$3,254	$4,210	$5,229	$6,314	$7,468	$8,696	$10,000

At first glance, that can look like a usable balance path. But the timing quickly breaks down under scrutiny.

In practice, CRFR is treated as the Reserve Requirements in the report year and compared to the fund's actual closing balance when discussing adequacy. In that setting, it is being used like a closing balance.

But in Year 10, CRFR equals $10,000, the full replacement cost. That amount must already exist before the replacement is paid. In that sense, CRFR behaves like a pre-expenditure balance, not a post-expenditure closing balance.

Could it instead be an opening balance? Not cleanly. If Year 10 opened with $10,000, that full amount would then earn a year of interest before the expenditure, which would overfund the component. So CRFR both must be and cannot be an opening balance.

A midpoint interpretation does not solve the problem either. If different components are treated as being replaced at different points within the year, then total fund-level CRFR would be adding together balances from different moments in time. If all components are instead forced onto one shared midpoint, the other formulas would also have to be changed to match that timing.

The cleanest interpretation of CRFR, given the set of formulas, is that it is a year-end balance after interest but before expenditures and contributions. In other words:

1. Start with the opening balance.
2. Earn interest on that balance.
3. The resulting pre-expenditure year-end amount is CRFR.
4. Apply any expenditures.
5. Add contributions.
6. Arrive at the closing balance.

That interpretation is at least internally readable. But it creates its own problem: CRFR can no longer be used as either the opening balance or the closing balance that practitioners compare against actual fund balances and later Reserve Requirements.

So the problem is deeper than a bad label.

In short, the Legacy Method does not define CRFR clearly enough to support a single coherent timing interpretation. Once a Benchmark balance has no stable timing meaning, every quantity built on it inherits that ambiguity.

CRFR already implies a contribution path of its own

The next problem is contribution logic.

To test whether CRFR can function as part of a year-by-year funding model, we have to force its sequence of values into some usable balance path. For illustration, the table below treats each year's CRFR as the opening balance. That is not because this interpretation is uniquely correct: it is because it is the simplest version to read. Other timing choices are explored below, but they do not change the central result.

When we look at a single component over its lifespan, moving from one year's CRFR to the next necessarily requires some contribution schedule.

That is the key issue. The problem is not merely that the implied contributions rise in an unusual way. The deeper problem is that once CRFR is treated as a year-by-year balance path, it already determines a contribution path before ARFA appears. ARFA then imposes a different contribution path on top of it. Once one method uses two incompatible contribution paths for the same component, it is no longer one coherent funding model.

Looking at the CRFR example above, here are the contributions required to move from one year's CRFR to the next:

	Year 0	Year 1	Year 2	Year 3	Year 4	Year 5	Year 6	Year 7	Year 8	Year 9	Year 10
Opening Balance / CRFR	$0	$734	$1,519	$2,358	$3,254	$4,210	$5,229	$6,314	$7,468	$8,696	$10,000
Expenditure	$0	$0	$0	$0	$0	$0	$0	$0	$0	$0	($10,000)
Interest	$0	$21	$44	$68	$94	$122	$152	$183	$217	$252	$290
Implied Contribution	$734	$764	$795	$828	$861	$897	$933	$971	$1,011	$1,052
Closing Balance	$734	$1,519	$2,358	$3,254	$4,210	$5,229	$6,314	$7,468	$8,696	$10,000	$290

Once CRFR is treated as a balance path, those contributions are not optional. They are the amounts required to move from one CRFR value to the next while earning interest along the way and paying the replacement at the end.

Those implied contributions are not flat. They are not CPI-linked. They are not stated anywhere as the intended contribution rule. And they are not consistent with ARFA, which is later introduced as though it were the contribution formula.

In this example, the contributions implied by CRFR rise by approximately 4.1% per year. That growth rate is not coming from any explicit contribution rule. It is an unintended consequence of the way the CRFR formula is structured.

So even before ARFA appears, the method is internally unstable.

Either CRFR is meant to function as a meaningful year-to-year target, in which case it already dictates a contribution path before ARFA appears, or it is not meant to function that way, in which case it cannot serve as the basis of a year-by-year funding model.

ARFA does not repair the starting problem

After calculating CRFR, the Legacy Method moves on to FRFA, FRFR, and ARFA.

That sequence sounds natural:

• If CRFR is already in the fund today, how much will it grow to? (FRFA)
• How much more will still be needed? (FRFR)
• What annual contribution will fill that gap? (ARFA)

But that sequence only works if CRFR was already a coherent reserve fund balance. It was not: ARFA does not solve the starting problem. It inherits it.

There is a second issue as well. In its common form, ARFA is calculated as a flat nominal contribution. That means it does not grow over time, even while replacement costs continue to grow and CRFR itself already implied a changing contribution path.

Let's see how this works with our fitness equipment example in Year 2:

	Year 0	Year 1	Year 2	Year 3	Year 4	Year 5	Year 6	Year 7	Year 8	Year 9	Year 10
Opening Balance	$-	$-	$1,519	$2,476	$3,461	$4,474	$5,517	$6,590	$7,695	$8,831	$10,000
Expenditure	$-	$-	$0	$0	$0	$0	$0	$0	$0	$0	($10,000)
Interest	$-	$-	$44	$72	$100	$130	$160	$191	$223	$256	$290
ARFA	$?	$?	$913	$913	$913	$913	$913	$913	$913	$913
Closing Balance	$-	$-	$2,476	$3,461	$4,474	$5,517	$6,590	$7,695	$8,831	$10,000	$290

Several things become clear immediately.

1. The ARFA contributions do not preserve the CRFR path. The Year 2 opening balance matches CRFR for Year 2, but once the flat ARFA contribution is used, no later opening or closing balance matches CRFR for the rest of the component's life. If we recalculated CRFR in any later year, this funding model would no longer follow its own stated requirement.
2. The ARFA contributions are flat in nominal dollars, so they decline in purchasing-power terms over time.
3. Even that flat contribution is not stable across valuations. In this example, recalculating ARFA at different effective ages gives values ranging from $876 to $1,052. So the Legacy Method does not produce one coherent long-run contribution path for the component. It produces different flat nominal paths depending on when the calculation is performed.
4. The model still leaves an additional $290 after the replacement. That happens because the balance path reaches $10,000 at the start of Year 10, then earns another year of interest before the expenditure is applied. In other words, this schedule effectively treats the expenditure as a year-end event.
5. But ARFA itself does not provide a contribution for that same replacement year. Once RL = 0, the annuity denominator collapses to zero, so the formula no longer defines a value. That means the Legacy Method does not supply one clear rule for how the old component's final year transitions into the next component cycle. The balance path and the contribution formula point in different directions.
6. The Year 2 opening balance of $1,519 must already have come from some earlier contribution pattern. It is not consistent with prior contributions of $913; it corresponds instead to earlier level contributions of about $749. So the method changes contribution logic depending on when you run the formulas.

The Legacy Method ends up mixing different logics:

• CRFR behaves like a moving age-based allocation of current cost. It already implies one rising contribution path of its own
• ARFA is then introduced as a different, flat nominal contribution path
• Later, RR values try to carry that mixed system forward into future years

That is not one coherent method. It is a chain of formulas that do not all belong to the same model.

At this point, we have seen four contribution schedules for the same component: three generated within the Legacy Method, and one from the Reserve Sense Benchmark Method.

	Year 0	Year 1	Year 2	Year 3	Year 4	Year 5	Year 6	Year 7	Year 8	Year 9
CRFR-Implied Contribution, OB or CB	$734	$764	$795	$828	$861	$897	$933	$971	$1,011	$1,052
CRFR-Implied Contribution, midpoint	$713	$742	$773	$804	$837	$871	$907	$944	$982	$1,021
ARFA	$?	$?	$913	$913	$913	$913	$913	$913	$913	$913
Ideal Contribution (Reserve Sense)	$808	$823	$839	$854	$871	$887	$904	$921	$939	$957

The two CRFR-implied contributions increase by about 4.1% per year. The ARFA contributions do not increase at all. The Ideal Contributions increase by 1.9% per year, which is the CPI inflation rate used in the Benchmark to preserve purchasing power.

So the Legacy Method is not simply too high or too low. It is internally inconsistent. Depending on when the component is evaluated, it may recommend a value below the Benchmark contribution or above it. That is exactly what we would expect from a method that mixes incompatible contribution logics instead of following one coherent funding model.

FRFA and FRFR are not stable Benchmark balances

FRFA and FRFR are not new reserve fund balance concepts. They are intermediate calculation steps within the Legacy Method.

For a single component, that is fine. FRFA asks how much the starting amount would grow to by that component's replacement year. FRFR asks how much more would still be needed in that same future year.

The problem appears when those values are treated as though they are meaningful reserve fund measures in their own right.

They are not.

Each component's FRFA and FRFR belongs to that component's own replacement year. One component's values might belong to Year 3, another's to Year 12, and another's to Year 27. Those are future-year amounts attached to different dates.

Because money has a time value, amounts from different future years cannot simply be added together and treated as though they form one meaningful present-day total, or one meaningful fund balance at any other single point in time.

A stable Benchmark balance must belong to one common date. FRFA and FRFR do not. They are future-value terms inside a formula, not year-by-year reserve fund balances.

That is why these quantities can be useful inside the ARFA calculation, but misleading when reported or totalled as though they were standalone measures of reserve fund adequacy.

Reserve Requirements inherit the same mismatch

Many practitioners then carry the Legacy Method forward by projecting later-year Reserve Requirements (RR).

This does not fix the earlier problem. It carries it forward.

A later RR value can only be meaningful if the method had already established a coherent balance path and a coherent contribution path. The Legacy Method never did that. CRFR had no stable timing meaning, CRFR already implied one contribution path of its own, and ARFA then overlaid a different one.

So later Reserve Requirements do not solve the mismatch. They simply extend the same mixed logic into later years.

There is a second problem as well. The RR shortcut typically carries forward the report-year ARFA as though it remains unchanged over time. But ARFA was only calculated for the current life cycle. For a repeating component, that contribution would need to increase after replacement if it were recalculated for the next generation. Holding it flat across future cycles causes the projected RR path to drift further and further away from a coherent Benchmark model.

Why Reserve Sense uses a different method

The Reserve Sense Benchmark Method does not change the goal of Benchmark funding: it corrects the implementation.

The goal is still to determine, for each year, how much the reserve fund should already contain, how much should be contributed, and what balance should remain after interest and expenditures.

What changes is how those values are calculated.

Instead of mixing a moving age-based target with contribution formulas that do not belong to the same framework, Reserve Sense calculates the Benchmark directly through one coherent year-by-year cash-flow model.

That model treats each year explicitly. Opening balance, interest, expenditures, contributions, and closing balance all belong to the same timing structure and the same set of assumptions.

It therefore produces a clear Ideal Opening Balance, Ideal Contribution, and Ideal Closing Balance. Each has a defined timing meaning, each belongs to the same model, and each follows logically from the year before.

This is not a competing funding philosophy. It is a correction to the implementation of Benchmark funding.

Key takeaways

The Legacy Method pursued a reasonable goal, but in its commonly used form it does not implement that goal through one internally consistent model.

It begins with CRFR, a moving age-based target that is not a stable Benchmark balance. CRFR does not preserve one clear timing meaning, and it already implies its own contribution path before ARFA is ever introduced.

The later FRFA, FRFR, ARFA, and RR formulas do not repair that starting problem. They build on it. ARFA adds a second and incompatible contribution logic, and later RR values carry that mismatch forward and compound the errors.

That is why the Legacy Method is not merely old-fashioned or approximate. In its commonly used form, it is mathematically inconsistent as a year-by-year funding model.

Reserve Sense developed a different method because the Benchmark should be calculated directly through one coherent year-by-year cash-flow model, with clear timing meanings for balances and contributions.

Where to go next

• To see the Reserve Sense Benchmark Method step by step, go to Walkthrough.
• For the exact formulas and variables that Reserve Sense uses in its models and software, see Formula Reference.