🛠️ Mutual Fund 計算機

A mutual fund pools money from many investors to buy a diversified portfolio of stocks, bonds, or other securities. Each investor owns shares representing a slice of the pool. Funds are managed actively (a portfolio manager picks holdings to beat a benchmark) or passively (the fund tracks an index like the S&P 500). They are popular for retirement accounts because a single purchase delivers instant diversification.

Fees compound just like returns — in the wrong direction. A 1% annual expense ratio over 30 years can consume roughly 25% of an investor's lifetime gains. This calculator separates four fee types so you can see exactly where your money goes:

• Sales charge (front-end load): a one-time percentage taken off every deposit before it enters the fund. A 2% load on a 1,000 contribution puts980 to work and pays $20 to the broker.
• Deferred sales charge (back-end load): a percentage taken when shares are redeemed. Often steps down with holding period (e.g., 5% in year 1, 0% by year 7).
• Operating expenses: ongoing annual fees expressed as a percentage of fund balance — covering management, marketing (12b-1), and administration. Deducted continuously.
• Transaction costs / spreads: not modeled here, but real funds incur trading costs that drag returns by another 0.1–0.5%/year.

The calculator simulates the fund balance month by month over the holding period. For each month it: (1) deducts the sales charge from the monthly contribution and adds the rest to the balance, (2) applies the monthly return (annual rate ÷ 12), then (3) deducts the operating expense (annual rate ÷ 12 of the current balance). At the end it deducts the deferred sales charge from the final balance.

The Net IRR is the annualized internal rate of return after every fee — the single rate that, applied to your contributions over time, would produce the actual final balance. It's the most honest measure of what the fund delivered.

For each month m from 1 to N (= years × 12 + months):

where r = annual return as decimal, opex = annual operating expense %. Initial investment receives the same sales-charge treatment at month 0. Annual contributions are added at the end of each twelfth month with their own sales charge.

20,000 initial,1,000/month contributions, 5% annual return, 5 years, 2% sales charge, 0.5% operating expense, no deferred charge:

• Total deposits: 20,000 +1,000 × 60 = $80,000
• Sales charges: 80,000 × 2% =1,600 (taken off every deposit)
• Operating expenses over 5 years (compounded monthly on average balance): roughly $1,323
• Ending value: ~$90,077
• Net return: ~$10,077, or a Net IRR of about 3.84%/year — well under the 5% gross because of the 1.16% drag from fees.

Removing the 2% sales charge alone would lift Net IRR by roughly 0.5%/year over the same period.

A front-end (Class A) load takes its bite upfront, leaving the rest to compound at the full return. A back-end (Class B / Class C) load keeps your full deposit invested but charges you on exit — typically as a contingent deferred sales charge that decreases the longer you hold. Class A is usually cheaper for long horizons, Class B for shorter ones, but the "no-load" funds pioneered by Vanguard are usually cheaper than either.

The OER is the single most important fee to compare across funds. Index funds typically charge 0.03–0.20%, actively managed funds 0.5–1.5%. Over a 30-year horizon, a 1% OER difference compounds into roughly a 25% smaller final balance — a six-figure swing on a typical retirement portfolio. Always know your fund's OER before investing.

• Mutual funds price once per day at NAV (net asset value). Bought from the fund company.
• ETFs (exchange-traded funds) trade on stock exchanges throughout the day. Generally lower expense ratios than mutual funds, more tax-efficient.
• Index funds are mutual funds or ETFs that track a market index passively. Lower fees because no active manager picks holdings.

This calculator works equally well for any of the three — the math depends only on contribution, return, and fee inputs.

• Constant return assumption. Real returns vary year to year. The 5% input represents an average; actual outcomes follow a distribution and depend on sequence-of-returns risk.
• Pre-tax math. If the account is taxable, capital gains and dividends will reduce realized returns further. Use this calc for IRA/401(k) or post-tax-adjusted projections.
• No inflation adjustment. The ending value is in nominal (today's) dollars; for "real" purchasing power, deflate by your assumed inflation rate.
• Excludes transaction costs. Bid-ask spreads, market-impact costs, and fund-level trading drag (especially in active funds) are not modeled here.