Savings Goal Calculator
How long to double your money, reach $1 million, or save for any target — with the Rule of 72 and exact math.
The Rule of 72
Divide 72 by your annual interest rate to find years to double: 72 ÷ Rate = Years to 2×
At 4%: doubles in 18.0 yearsAt 6%: doubles in 12.0 yearsAt 8%: doubles in 9.0 yearsAt 5%: doubles in 14.4 yearsAt 7%: doubles in 10.3 yearsAt 10%: doubles in 7.2 years
Years to Double Your Money — by Rate
| Annual Rate | Rule of 72 (approx) | Exact Years | $10K becomes | $50K becomes |
|---|---|---|---|---|
| 2% | 36.0 years | 34.7 years | $20,000 | $100,000 |
| 3% | 24.0 years | 23.1 years | $20,000 | $100,000 |
| 4% | 18.0 years | 17.4 years | $20,000 | $100,000 |
| 5% | 14.4 years | 13.9 years | $20,000 | $100,000 |
| 6% | 12.0 years | 11.6 years | $20,000 | $100,000 |
| 7% | 10.3 years | 9.9 years | $20,000 | $100,000 |
| 8% | 9.0 years | 8.7 years | $20,000 | $100,000 |
| 10% | 7.2 years | 7.0 years | $20,000 | $100,000 |
| 12% | 6.0 years | 5.8 years | $20,000 | $100,000 |
How Long to Reach $1 Million?
Monthly contributions only, no initial deposit, at 7% APY:
| Monthly Savings | Years to $1M | Total Deposited | Interest Earned |
|---|---|---|---|
| $500/mo | 36.4 years | $218,260 | $781,740 |
| $1,000/mo | 27.5 years | $330,414 | $669,586 |
| $1,500/mo | 22.7 years | $409,266 | $590,734 |
| $2,000/mo | 19.6 years | $469,447 | $530,553 |
| $3,000/mo | 15.5 years | $557,006 | $442,994 |
How Much Do You Need to Save Monthly?
To reach $100,000 in 10 years at 5% APY:
$643.99/month
You'd deposit $77,279 — interest covers the rest
Saving for a Big Purchase
Monthly savings needed at 4.5% APY (HYSA) for common goals:
| Purchase Goal | Save in 1yr | Save in 2yr | Save in 3yr | Save in 5yr |
|---|---|---|---|---|
| Emergency fund (3 months) ($15,000) | $1,224.43/mo | $598.47/mo | $389.95/mo | $223.40/mo |
| New car down payment ($5,000) | $408.14/mo | $199.49/mo | $129.98/mo | $74.47/mo |
| Used car (cash) ($20,000) | $1,632.57/mo | $797.96/mo | $519.94/mo | $297.86/mo |
| Home down payment (10%) ($40,000) | $3,265.14/mo | $1,595.91/mo | $1,039.88/mo | $595.72/mo |
| Home down payment (20%) ($80,000) | $6,530.28/mo | $3,191.82/mo | $2,079.75/mo | $1,191.44/mo |
| Dream vacation ($10,000) | $816.29/mo | $398.98/mo | $259.97/mo | $148.93/mo |
Model Your Savings Goal
Frequently Asked Questions
Using the Rule of 72: 72 ÷ 7 = 10.3 years. The actual calculation (solving for t in FV = PV×e^(rt)) gives 9.9 years at 7% compounded monthly. At 5%: 14.4 years. At 10%: 7.3 years. The Rule of 72 is accurate within 1% for rates between 3–20% and is easy to do in your head.