Round-Up Savings Engine
Example: Average transactions per month: 60 txn · Average round-up per transaction: 0.5 $ · Annual investment return: 7 % · Years to compound: 20 yr
| Future value after compounding | $15,628 |
| Monthly round-up total | $30 |
| Total contributed over period | $7,200 |
| Investment gain above contributions | $8,428 |
| Annual round-up total | $360 |
Worked example
60 transactions a month at an average $0.50 round-up generates $30 a month — $360 a year. Invested at 7% for 20 years, that $360 a year grows to $15,672. Total contributions were $7,200; the remaining $8,472 is pure investment growth. This required zero change in lifestyle or income.
Frequently asked questions
How accurate is the average round-up assumption?
The average round-up on a random transaction is $0.50 — the midpoint between $0.01 and $0.99. In practice it varies: purchases ending in round numbers ($5.00, $10.00) contribute $0, while $4.01 purchases contribute $0.99. Over many transactions, the $0.50 average is a reliable estimate consistent with how apps like Acorns describe their user experience.
Should round-up savings go to a HYSA or be invested?
Varies by timeline. If the round-up account is your emergency fund supplement, a HYSA protects principal. If you have a fully funded emergency fund and this is long-term wealth building, a diversified low-cost index fund at 7% historical average outperforms HYSA over 10+ years. Many people use a separate round-up portfolio for investing.
Is the round-up amount taxable?
Round-up contributions are after-tax dollars — they are not deductible. The investment gains in a taxable account are subject to capital gains tax when sold. Using a Roth IRA for round-up investing shelters the growth from taxes entirely, significantly improving the long-term outcome.
How does this compare to just increasing my savings rate by $30 a month?
The math is identical — $30 a month invested at 7% for 20 years is $15,672 either way. The behavioral difference is significant: automated round-ups happen invisibly with no willpower required, while committing to an extra $30 a month requires ongoing discipline. Both are good; the round-up approach has lower friction.