One Fund vs Multi-Fund Calculator
The case for assembling your own portfolio from several funds is usually argued on fees, and fees are rarely where the answer lies. A blended fee across four funds is often close to what a single diversified fund charges, sometimes a little under and sometimes a little over, and the gap is measured in hundredths of a percent. What separates the two options is everything around the fee: the trades needed to hold the weights steady, the time those trades take, and whether the rebalancing actually happens once the novelty wears off. This page prices all of it. It works out the blended fee properly, weighted by what you hold in each fund rather than averaged across the funds, adds the annual cost of the trades, and converts the result into an hourly rate for the work involved. That hourly figure is the one that decides it for most people, because a fee difference of three hundredths of a percent is impossible to judge and a rate per hour is not. It also finds the portfolio size at which the do-it-yourself version starts to pay at all, since fee savings scale with the balance while trading costs do not, and below that size the arithmetic is simply against you. None of this settles whether control over your own weights is worth having. That is the real product on offer, and this page prices it rather than judging it.
Annual fee saving = (single fund fee − blended fee) × portfolio value. A negative figure means the single fund is cheaper.
Trading cost = trades a year × cost per trade. It is a fixed dollar amount, so it does not shrink as a percentage until the portfolio grows.
Net money difference = fee saving − trading cost, before any value on your time.
Hourly rate = net money difference / hours a year. This is what the extra work pays, and it is the figure most people can actually judge.
Break-even portfolio size = trading cost / fee gap, the value at which the fee saving first covers the trades.
Long-run difference compounds each option at gross return less its fee, then subtracts the future value of the annual trading costs from the multi-fund side. Time is reported in hours, not compounded into the balance, because it is not money taken out of the portfolio.
Excluded: tax differences between fund types, bid-ask spreads, foreign exchange costs on international trades, fixed membership or platform fees, and any difference in tracking quality between the funds.
All fees are user-entered. No provider is named, ranked or recommended, and the defaults are illustrative rather than an offer or a market survey.
Not financial advice. Last verified: August 2026.
Where the blended fee comes from
| Holding | Weight | Fee | Contribution | Cost a year |
|---|---|---|---|---|
| Fund 1 | 50% | 0.20% | 0.10% | $100.00 |
| Fund 2 | 30% | 0.30% | 0.09% | $90.00 |
| Fund 3 | 10% | 0.45% | 0.05% | $45.00 |
| Fund 4 | 10% | 0.35% | 0.04% | $35.00 |
| Multi-fund blended | 100% | 0.27% | 0.27% | $270.00 |
| Single fund | 100% | 0.30% | 0.30% | $300.00 |
| Fee saving a year | 0.03% | $30.00 |
Contribution is weight times fee. Note that the blended 0.27% is well below the simple average of the four fees, because most of the money sits in the cheapest one.
The full annual comparison
| Single fund fee at 0.30% | $300.00 |
| Multi-fund blended fee at 0.27% | $270.00 |
| Fee saving | $30.00 |
| Less trading, 4 trades at $3.00 | -$12.00 |
| Net money difference a year | $18.00 |
| Hours a year it takes | 3 |
| What that works out at | $6.00 an hour |
A fee difference of three hundredths of a percent is impossible to judge in the abstract. An hourly rate is not, which is the point of expressing it this way.
How the answer changes with portfolio size
| Portfolio | Fee saving | Less trades | Net a year | Per hour |
|---|---|---|---|---|
| $10,000.00 | $3.00 | -$12.00 | -$9.00 | -$3.00 |
| $50,000.00 | $15.00 | -$12.00 | $3.00 | $1.00 |
| $100,000.00 | $30.00 | -$12.00 | $18.00 | $6.00 |
| $250,000.00 | $75.00 | -$12.00 | $63.00 | $21.00 |
| $500,000.00 | $150.00 | -$12.00 | $138.00 | $46.00 |
Fee savings scale with the balance and trading costs do not, so this decision is worth revisiting as the portfolio grows rather than settling once.
How sensitive it is to the single fund's fee
| If the single fund charged | Fee saving | Net a year | Per hour | Which wins |
|---|---|---|---|---|
| 0.20% | -$70.00 | -$82.00 | -$27.33 | Single fund |
| 0.25% | -$20.00 | -$32.00 | -$10.67 | Single fund |
| 0.30% | $30.00 | $18.00 | $6.00 | Multi-fund, barely |
| 0.35% | $80.00 | $68.00 | $22.67 | Multi-fund |
| 0.50% | $230.00 | $218.00 | $72.67 | Multi-fund clearly |
A five hundredth of a percent on the single fund's fee flips the decision entirely, which makes it the first number to check rather than the last.
The Fee Gap Is Smaller Than The Argument Suggests
Assembling a portfolio from cheap component funds sounds like it should be meaningfully cheaper than buying one diversified fund. On realistic numbers it usually is not.
On the worked example the blended cost of four funds is 0.27% against 0.30% for the single fund. That is a saving of three hundredths of a percent, or $30.00 a year on $100,000.00, and the trades needed to maintain it eat $12.00 of that immediately.
Worked Example: $100,000 Across Four Funds
Half the money in a fund charging 0.20%, 30% in one charging 0.30%, and 10% each in funds charging 0.45% and 0.35%.
The blended fee is 0.27%, costing $270.00 a year against $300.00 for the single fund. Four rebalancing trades at $3.00 each cost $12.00.
The net money difference is $18.00 a year. Over three hours of work that is $6.00 an hour.
Across twenty years the multi-fund portfolio ends at $367,422.66 against $365,837.64, a difference of $1,585.02 for sixty hours of work.
Blended Is Not Averaged
The four fees average to 0.325%. The blended fee is 0.27%, because most of the money sits in the cheapest fund and the expensive ones hold 10% each.
That gap of a fifth matters, and averaging the fees is a common enough mistake to be worth naming. Always weight by what you actually hold.
It also points at the practical version of this decision: a portfolio's cost is dominated by where the bulk of the money sits, so a small allocation to an expensive specialist fund costs far less than its headline fee suggests.
Size Decides It More Than Anything Else
Fee savings are a percentage of the balance. Trading costs are a fixed number of dollars. The two scale completely differently, so the same decision has different answers at different sizes.
Below $40,000.00 on the worked example, the do-it-yourself portfolio loses money outright: the $12.00 of trades exceeds the fee saving before any value is put on your time.
At $250,000.00 it pays $21.00 an hour, and at $500,000.00 it pays $46.00. Those are rates worth taking.
The implication is that this is not a decision to settle once. It is worth revisiting each time the portfolio changes materially in size.
The Number That Actually Flips It
The sensitivity table is blunt. If the single fund charged 0.25% instead of 0.30%, the multi-fund portfolio's $18.00 annual advantage becomes a $32.00 disadvantage, and the twenty-year figure moves from $1,585.02 ahead to $1,858.95 behind.
Five hundredths of a percent decides the whole question. Check the single fund's total fee, including any administration charge or fixed membership fee, before doing anything else, because those are frequently quoted separately from the management fee and all come out of the same return.
Our fund fee drag calculator shows what a fee difference does over a long horizon on its own.
The Cost That Is Not On This Page
A multi-fund portfolio only holds its allocation if you rebalance it. A portfolio left alone drifts towards whatever has done best, which is usually the opposite of what rebalancing is for.
The trades in the calculation above assume the rebalancing happens. If it does not, the fee saving is still real and the allocation is not the one you chose, which means you are paying for control you are not using.
Our rebalancing threshold calculator works out how often it genuinely needs doing, and our portfolio rebalance calculator works out the trades.
What You Are Actually Buying
The fee comparison is close enough that it is not really the point. The difference between these two options is control over the weights.
A single global fund gives you the market's allocation, which for a New Zealander means a large weight to the United States and almost nothing in the home market. Assembling it yourself lets you set those weights on purpose.
Whether that control is worth $6.00 an hour is a judgement rather than a calculation. What this page does is make sure the judgement is made against the right number. Our home bias calculator and fund overlap calculator deal with whether the weights you have chosen are the ones you think you have.
Related NZ Portfolio Calculators
- Fund Overlap Calculator: whether your funds duplicate each other.
- Fund Fee Drag Calculator: what a fee difference costs over a long horizon.
- Rebalancing Threshold Calculator: how often rebalancing is actually needed.
- Portfolio Rebalance Calculator: the trades to get back to target.
- Home Bias Calculator: your NZ weight against the global benchmark.
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