Client Portfolio Projection Calculator NZ 2026/27
Almost every portfolio projection ever shown to a client is a single line on a chart curving pleasantly upward to a specific number, and almost every one of them is misleading in the same three ways. The first is that a single line implies a precision that does not exist. Run the same assumptions honestly and the answer is not a number but a range so wide that the good case is nearly three times the poor one, and a client who was shown only the middle will experience anything else as a failure. The second is inflation. A projection in nominal dollars is arithmetically correct and practically useless for the question the client is actually asking, which is what the money will buy, and over twenty years the gap between those two figures is roughly a third of the total. The third is subtler and catches professionals as often as clients. The average outcome and the typical outcome are different numbers, because compounding produces a skewed distribution with a long tail of very good results pulling the average upward. More than half of all outcomes fall below the average, so quoting it sets an expectation that most clients will not meet. Related to this, raising volatility while holding the expected return constant leaves the average untouched and pushes the median down, which means two portfolios advertised with the same expected return will not deliver the same typical result. This page shows all of it rather than the reassuring line.
The mean and variance of the balance are computed exactly, by recursion. With annual returns independent and identically distributed, the balance evolves as W₁ = W₀(1+R) + C, giving E[W₁] = E[W₀]m₁ + C and E[W₁²] = E[W₀²]m₂ + 2Cm₁E[W₀] + C², where m₁ = 1+r and m₂ = (1+r)² + s².
Percentiles come from a lognormal fitted to those two moments. A portfolio receiving contributions is not exactly lognormal, so this is a deliberate approximation. It is stated here rather than presented as exact.
Poor and good cases are the 10th and 90th percentiles, so 80% of outcomes fall between them.
Today's money divides each nominal figure by inflation compounded over the period.
The average exceeds the median because the distribution is right-skewed. This follows from the arithmetic rather than from any assumption, and it is why the median is used as the headline.
Volatility lowers the median while leaving the average unchanged, which the moment recursion shows directly: the mean depends only on m₁ and not on volatility at all.
Excluded: tax and fees, which should be netted off the return you enter; contribution increases over time; and any withdrawals.
Known limits: returns are assumed independent with constant volatility, and real markets have fatter tails than the model allows.
Not financial advice. Last verified: August 2026.
The range at each horizon
| After | Put in | Poor case | Median | Good case | Median in today's money |
|---|---|---|---|---|---|
| 5 years | $470,000.00 | $453,504.19 | $601,410.85 | $797,556.06 | $544,716.34 |
| 10 years | $590,000.00 | $638,142.12 | $937,631.24 | $1,377,674.83 | $769,184.19 |
| 15 years | $710,000.00 | $869,935.19 | $1,385,921.38 | $2,207,955.37 | $1,029,760.00 |
| 20 years | $830,000.00 | $1,158,154.69 | $1,982,703.47 | $3,394,290.14 | $1,334,302.60 |
| 25 years | $950,000.00 | $1,516,926.92 | $2,776,355.23 | $5,081,423.68 | $1,692,274.22 |
| 30 years | $1,070,000.00 | $1,964,877.09 | $3,831,080.83 | $7,469,770.19 | $2,115,028.20 |
Note how the poor case at 5 years sits below what was put in. Early on, a bad run is not recoverable by contributions alone.
How wide the range gets
| After | Poor case | Good case | Spread | Good as a multiple of poor |
|---|---|---|---|---|
| 5 years | $453,504.19 | $797,556.06 | $344,051.88 | 1.76x |
| 10 years | $638,142.12 | $1,377,674.83 | $739,532.71 | 2.16x |
| 20 years | $1,158,154.69 | $3,394,290.14 | $2,236,135.45 | 2.93x |
| 30 years | $1,964,877.09 | $7,469,770.19 | $5,504,893.10 | 3.80x |
Longer horizons narrow the range of annual returns and widen the range of dollar outcomes. Both are true, and only the first usually gets mentioned.
Volatility lowers the median
| Volatility | Poor case | Median | Good case | Average |
|---|---|---|---|---|
| 6.00% | $1,620,930.75 | $2,118,376.58 | $2,768,483.07 | $2,165,083.18 |
| 9.00% | $1,378,490.17 | $2,061,032.49 | $3,081,527.17 | $2,165,083.18 |
| 12.00% | $1,158,154.69 | $1,982,703.47 | $3,394,290.14 | $2,165,083.18 |
| 15.00% | $960,807.05 | $1,885,360.30 | $3,699,580.92 | $2,165,083.18 |
| 18.00% | $786,694.09 | $1,771,536.23 | $3,989,276.93 | $2,165,083.18 |
The average column never moves, because the mean does not depend on volatility at all. The median falls steadily, which is the outcome a client is more likely to experience.
The Average Is Not The Typical Outcome
This is the error most worth correcting, because it is made in good faith by people who know the arithmetic.
On the worked example the average outcome is $2,165,083.18 and the median is $1,982,703.47. The distribution is right-skewed, so a small number of excellent outcomes pull the average above the middle.
More than half of all clients on these assumptions will finish below the average. Quoting it as the expected result guarantees that most people are disappointed by something that was always likely.
Worked Example: $350,000 Plus $24,000 A Year
Put in over 20 years: $830,000.00.
Poor case: $1,158,154.69, with one outcome in ten falling below it.
Median: $1,982,703.47.
Good case: $3,394,290.14, with one in ten above.
The good case is 2.93 times the poor one. That is the honest answer, and no single number represents it.
What It Buys, Not What It Says
The nominal median of $1,982,703.47 becomes $1,334,302.60 in today's money at 2.00% inflation.
Both figures are correct. Only the second answers the question the client is actually asking, which is what they will be able to do with the money.
Over 20 years the difference is about a third of the total, and at 30 years the nominal figure of $3,831,080.83 falls to $2,115,028.20. Presenting the nominal number alone is the single easiest way to overstate a plan. Our investment time horizon risk calculator works the same distribution from the risk side.
Volatility Is Not Free
Two portfolios can advertise the same expected return and deliver quite different typical outcomes.
Holding the expected return at 6.50%, a portfolio with 6.00% volatility has a median of $2,118,376.58. At 18.00% volatility the median falls to $1,771,536.23, a difference of nearly $350,000.00.
The average is identical in both cases, because the mean does not depend on volatility. What changes is where the middle sits, and the middle is what most people get. This is the quantitative argument for diversification, and our index concentration calculator measures the input it depends on.
The Early Years Are The Fragile Ones
Look at the five year row: the poor case of $453,504.19 is below the $470,000.00 that was put in.
A client four years into a plan, having contributed diligently and holding less than they deposited, is in an entirely ordinary tenth-percentile outcome rather than a broken plan. Whether they know that in advance largely determines whether they stay invested.
Showing the range at the start is what makes that conversation possible later. A client shown only the median has no framework for a normal bad run, and our adviser fee impact calculator puts a number on what abandoning a plan at that point costs.
Using This Properly
Lead with the median in today's money, show the range beside it, and say plainly that one outcome in ten falls below the poor case.
Enter returns net of fees and tax rather than gross, since a projection built on gross returns describes a portfolio nobody owns. Our fund fee drag calculator shows how much that adjustment matters.
And treat the contribution assumption as the weakest part of the model. Markets are uncertain in ways this arithmetic captures. Whether someone keeps contributing $24,000.00 a year for two decades through job changes, illness and competing priorities is uncertain in ways it does not.
Related NZ Investment Projection Calculators
- Investment Time Horizon Risk Calculator: the same distribution from the risk side.
- Adviser Fee Impact Calculator: what fees and abandoned plans cost.
- Fund Fee Drag Calculator: converting gross returns to net.
- Index Concentration Calculator: what drives the volatility input.
- Early Retirement Bridge Calculator: projections with a fixed deadline.