“How much should I invest?” is one of the most common questions from new investors. There’s no single right answer — but there are frameworks to find the right number for your situation.
Common framework: invest 10–20% of take-home pay, after building a 3-month emergency fund. Even $200/month invested at 8% average return over 30 years grows to $298,000. The most important factor is starting — amount matters less than consistency. First priority: max KiwiSaver to get employer contribution; second priority: invest surplus in index funds.
Step 1: Get the Order Right
Before deciding how much to invest in index funds and shares, sort priorities:
| Priority | Action |
|---|---|
| 1 | Eliminate high-interest debt (credit card, buy-now-pay-later) |
| 2 | Build emergency fund (3 months of expenses) |
| 3 | Contribute enough to KiwiSaver to maximise employer match |
| 4 | Invest surplus in index funds / term deposits |
KiwiSaver employer match is free money. If your employer contributes 3.5% and you contribute 3.5% (the minimum rose from 3% on 1 April 2026), you immediately double the employer portion. This is a 100% return on your KiwiSaver contributions before any investment growth — always prioritise this first.
The 50/30/20 Framework
A simple starting framework for NZ adults:
| Category | Allocation | What goes here |
|---|---|---|
| Needs | 50% | Rent/mortgage, groceries, utilities, transport, insurance |
| Wants | 30% | Dining out, entertainment, travel, subscriptions |
| Savings/Investing | 20% | KiwiSaver, emergency fund, index funds |
Example on $80,000 salary (~$5,194/month after PAYE and ACC, 2026–27):
- Needs (50%): $2,597/month
- Wants (30%): $1,558/month
- Saving/Investing (20%): $1,039/month
This is a starting point — adjust based on your rent (Auckland rent is often 40%+ of income) and goals.
How Much Does Monthly Investing Actually Grow To?
Assumed average return: 8% p.a. (global diversified index fund, long-term estimate)
| Monthly investment | 10 years | 20 years | 30 years |
|---|---|---|---|
| $100 | $18,300 | $58,900 | $149,000 |
| $200 | $36,600 | $117,800 | $298,000 |
| $500 | $91,500 | $294,500 | $745,000 |
| $1,000 | $183,000 | $589,000 | $1,490,000 |
| $2,000 | $366,000 | $1,178,000 | $2,980,000 |
Approximate. 8% nominal, not adjusted for inflation or taxes. Tax drag (PIR 28%) reduces returns — effective after-tax growth closer to 6.5–7.0%.
The key insight: Even modest amounts invested consistently over 30 years produce significant wealth. Starting at $200/month and not increasing this — just being consistent — grows to nearly $300,000.
Setting Your Investment Amount
Method 1: Fixed percentage (simplest)
Choose 10%, 15%, or 20% of your take-home pay and invest that amount automatically. Increase by 1% each year when you get a pay rise.
Example: $5,194/month take-home (on $80,000) → invest $779/month (15%)
Method 2: Goal-based
Calculate backwards from a specific goal:
Goal: $500,000 in 25 years (retirement supplement) At 7% real return (after inflation, after tax): Monthly amount = 500,000 ÷ (FV factor) ≈ $780/month
Use an online compound interest calculator with your specific return assumption and time horizon.
Method 3: Pay yourself first
Set up an automatic transfer to an investment account on payday — before you can spend it. Start with any amount and increase each 6 months. This removes the decision from willpower and makes investing automatic.
What About KiwiSaver?
KiwiSaver contributions count toward your savings/investing allocation. If you contribute the 3.5% minimum of your salary ($2,800/year on $80,000), that’s about $233/month going to KiwiSaver automatically — plus your employer’s 3.5% (another ~$233/month) = ~$467/month total.
For most NZ employees on moderate incomes, maximising KiwiSaver (especially with employer match) and then investing surplus into index funds is an effective split.
Government contribution: If you contribute at least $1,042.86/year to KiwiSaver, IRD adds $260.72 (maximum, halved from $521.43 on 1 July 2025) as a government top-up. This is free money: if you’re not hitting the threshold, prioritise it.
The Impact of Starting Early
Two investors, same $500/month:
| Investor | Start age | Stop age | Total contributed | Portfolio at 65 |
|---|---|---|---|---|
| Early starter | 25 | 65 | $240,000 | $1,745,000 |
| Late starter | 35 | 65 | $180,000 | $792,000 |
| Very late | 45 | 65 | $120,000 | $349,000 |
8% p.a. assumed return. The 10-year difference between starting at 25 vs 35 — investing the same $500/month — produces more than double the final portfolio. This is the power of compound growth.
The single most important decision is to start now — even at a small amount — rather than waiting until you can invest “the right amount.”
Common Questions About Investment Amounts
Can I start with just $50/month? Yes. Kernel accepts $1 minimum. InvestNow accepts $50/month via auto-invest. Sharesies accepts any amount. Starting small and building the habit is more valuable than waiting until you have a larger amount.
Should I split between KiwiSaver and index funds? Both. KiwiSaver is locked until 65 (with limited exceptions) — building a separate investment portfolio gives flexibility for mid-life goals (house deposit, career change, early retirement). Target KiwiSaver for retirement; investment portfolio for medium-term goals.
What if my income is irregular (contractor, freelancer)? Instead of a fixed monthly amount, invest a fixed percentage of every payment received. When you receive $5,000, invest $750 (15%) immediately. This naturally scales investment with income.
How much should I keep as cash vs invest? Keep 3–6 months of living expenses as cash (high-interest savings account or 90-day term deposit). Everything above this threshold — money you don’t need for 5+ years — can be invested.