Two savers, both earning $70,000 a year, both starting at age 30 with nothing invested. One saves 20% of gross pay and earns 4% a year. The other saves 10% and earns 8%. Over 30 years, which one ends up with more money?
The answer is not the one most people guess. The 8% path wins, but by a smaller margin than the return gap suggests — and the 20% path gets there with far less market risk. This article builds the year-by-year ledger for both paths, states every assumption, and shows exactly where the ending balances come from. You can rebuild the math in a spreadsheet and get the same numbers.
The two paths, stated plainly
Path A — the high savings rate: Save 20% of a $70,000 salary, or $14,000 a year, invested at a 4% annual return.
Path B — the high return: Save 10% of a $70,000 salary, or $7,000 a year, invested at an 8% annual return.
Both savers contribute at the start of each year. Both salaries stay flat in nominal terms so the arithmetic is transparent. Both returns are nominal, before inflation and before taxes. We will handle inflation and taxes separately, because they change the comparison in ways that matter.
The year-by-year ledger
Here is what happens over 30 years. Each row shows the balance at the end of that year, after the contribution and after the return is applied.
| Year | Age | Path A: 20% saved, 4% return | Path B: 10% saved, 8% return |
|---|---|---|---|
| 1 | 31 | $14,560 | $7,560 |
| 2 | 32 | $29,702 | $15,725 |
| 3 | 33 | $45,450 | $24,543 |
| 4 | 34 | $61,828 | $34,066 |
| 5 | 35 | $78,861 | $44,351 |
| 6 | 36 | $96,576 | $55,459 |
| 7 | 37 | $114,999 | $67,456 |
| 8 | 38 | $134,159 | $80,412 |
| 9 | 39 | $154,085 | $94,405 |
| 10 | 40 | $174,808 | $109,517 |
| 11 | 41 | $196,361 | $125,839 |
| 12 | 42 | $218,775 | $143,466 |
| 13 | 43 | $242,086 | $162,503 |
| 14 | 44 | $266,329 | $183,063 |
| 15 | 45 | $291,542 | $205,268 |
| 16 | 46 | $317,764 | $229,250 |
| 17 | 47 | $345,035 | $255,150 |
| 18 | 48 | $373,396 | $283,122 |
| 19 | 49 | $402,892 | $313,332 |
| 20 | 50 | $433,568 | $345,958 |
| 21 | 51 | $465,471 | $381,195 |
| 22 | 52 | $498,650 | $419,251 |
| 23 | 53 | $533,156 | $460,351 |
| 24 | 54 | $569,042 | $504,739 |
| 25 | 55 | $606,364 | $552,678 |
| 26 | 56 | $645,178 | $604,452 |
| 27 | 57 | $685,545 | $660,368 |
| 28 | 58 | $727,527 | $720,757 |
| 29 | 59 | $771,188 | $785,978 |
| 30 | 60 | $816,596 | $856,416 |
At the end of 30 years, Path A holds about $816,600. Path B holds about $856,400. The 8% return path wins by roughly $40,000 — about 5% more than the 20% savings path.
That is the central finding. Doubling the return from 4% to 8% beats doubling the savings rate from 10% to 20%, but only narrowly. And the 20% saver got there with half the market exposure.
Why the gap is so small
The 20% saver contributes $14,000 a year. The 10% saver contributes $7,000. Over 30 years, the 20% saver puts in $420,000 of principal. The 10% saver puts in $210,000. That extra $210,000 of contributions compounds at 4% and does most of the work.
The 8% return on the smaller base has to overcome a $210,000 contribution deficit. It almost does, but not quite by a wide margin.
This is the arithmetic of compounding: the savings rate controls the base, and the return controls the growth rate. When you double the savings rate, you double the base. When you double the return, you accelerate the growth on a smaller base. Over 30 years, those two effects are closer in size than intuition suggests.
What inflation does to both paths
The numbers above are nominal. To see purchasing power, we need an inflation assumption. For this comparison, we use a stated 3% annual inflation assumption. It is not a forecast; it is a round-number placeholder that makes the real-balance arithmetic easy to follow.
If we subtract 3% inflation from both returns, Path A’s real return is about 1% and Path B’s real return is about 5%. The real ending balances are very different:
- Path A real balance: roughly $816,600 / (1.03^30) ≈ $336,000 in today’s dollars
- Path B real balance: roughly $856,400 / (1.03^30) ≈ $352,000 in today’s dollars
The gap in real terms is still about $16,000. Inflation shrinks both piles, but it does not change the ranking. The 8% path still wins, and the 20% path still gets most of the way there with less risk.
What taxes do to both paths
Taxes depend on the account type. If both savers use a traditional 401(k) or traditional IRA, contributions are pre-tax and withdrawals are taxed as ordinary income. If both use a Roth account, contributions are after-tax and withdrawals are tax-free.
For a $70,000 salary, the 20% saver contributes $14,000 a year. The 10% saver contributes $7,000. Both are within the elective deferral limit for most years, though the limit has changed over time.
If both use traditional accounts, the 20% saver gets a larger current tax deduction. At a 22% marginal rate, that is $3,080 a year in tax savings, versus $1,540 for the 10% saver. Over 30 years, that is an extra $46,200 in nominal tax savings for the 20% saver, before accounting for the time value of those savings.
If both use Roth accounts, the 20% saver pays more tax upfront but gets a larger tax-free balance later. The ranking of ending balances does not change, but the after-tax comparison depends on future tax rates, which are not knowable.
The key point: taxes affect both paths, but they do not flip the ranking. The 8% return path still ends with more money, and the 20% savings path still ends with less market risk.
What the 4% and 8% assumptions mean
A 4% nominal return is roughly what you might expect from a conservative portfolio heavy in bonds and cash. It is not a prediction; it is a stress-test assumption for a low-return environment.
An 8% nominal return is roughly what you might expect from a diversified stock-heavy portfolio over a long horizon. It is not guaranteed. The S&P 500 has returned about 10% annually over long periods, but that includes decades of high returns and decades of low returns. An 8% assumption is a reasonable middle ground for a 30-year horizon, but it is still an assumption.
The comparison is not about which return is more likely. It is about which lever — savings rate or return — has more control over the ending balance. The answer is that both matter, but the savings rate is the one you control directly.
The risk-adjusted view
Path A earns 4% with low volatility. Path B earns 8% with high volatility. Over 30 years, the 8% path has a wider range of outcomes. In a bad sequence of returns, the 8% path could end up below the 4% path. In a good sequence, it could end up far above.
The 20% saver does not need the 8% return to reach a meaningful balance. The 10% saver does. That is the quiet argument for a high savings rate: it reduces your dependence on market returns you cannot control.
What if the 20% saver also earns 8%?
If the 20% saver earns 8% instead of 4%, the ending balance is dramatically higher. Saving $14,000 a year at 8% for 30 years produces about $1.71 million. That is nearly double the 10% saver’s $856,000.
This is the real lesson: the savings rate and the return are not competing levers. They are multiplicative. A high savings rate plus a high return is far better than either alone. But if you have to choose one to focus on first, the savings rate is the one you can control.
How to rebuild this in a spreadsheet
Open a spreadsheet and set up four columns: Year, Age, Path A balance, Path B balance. In the first row, Year 1, Age 31, Path A balance is $14,000 × 1.04 = $14,560. Path B balance is $7,000 × 1.08 = $7,560.
For each subsequent row, Path A balance is (previous balance + $14,000) × 1.04. Path B balance is (previous balance + $7,000) × 1.08. Drag the formulas down 30 rows. The final row should match the table above.
If you want to add inflation, divide the final balances by (1 + inflation rate)^30. If you want to add taxes, multiply the final balances by (1 − tax rate) for traditional accounts, or leave them as-is for Roth accounts.
Frequently asked questions
Does the 20% saver really end up with less money?
Yes, in this comparison. The 8% return path ends with about $856,000, and the 4% return path ends with about $816,000. The difference is about $40,000, or roughly 5%.
What if the 20% saver earns 6% instead of 4%?
At 6%, the 20% saver ends with about $1.17 million. That beats the 10% saver at 8% by a wide margin. The return assumption matters a lot.
What if the 10% saver earns only 6%?
At 6%, the 10% saver ends with about $585,000. That is well below the 20% saver at 4%. The savings rate provides a floor that the return cannot.
Should I focus on saving more or earning more?
Both matter. But the savings rate is the lever you control directly. The return is the lever the market controls. A high savings rate gives you more options and less dependence on market outcomes.
Does this account for inflation?
The main table is nominal. Inflation reduces both ending balances by roughly the same factor, so the ranking does not change. In real terms, the gap is smaller but still favors the 8% path.
Does this account for taxes?
The main table is pre-tax. Taxes affect both paths, but they do not flip the ranking. The 20% saver gets a larger current deduction in a traditional account, which partially offsets the lower return.
The bottom line
On a $70,000 salary over 30 years, saving 10% at 8% ends with about $856,000. Saving 20% at 4% ends with about $816,000. The 8% path wins by about $40,000, or 5%.
But the 20% saver got there with half the market risk and twice the contribution discipline. And if the 20% saver also earns 8%, the ending balance is about $1.71 million — nearly double the 10% saver’s result.
The arithmetic does not say that returns do not matter. It says that the savings rate is the lever you control, and it does more work than most people expect. If you want to see how a small change in weekly savings compounds over time, the article on what a ten-dollar weekly bump actually does to your retirement number walks through a similar ledger with smaller numbers.
Run the numbers for your own salary and your own assumptions. The spreadsheet will tell you the same thing the table does: the base you build matters as much as the rate it grows.