Saving Calculator Project how your savings grow with compound interest — set goals, compare strategies, and optimize your...
Saving Calculator
Project how your savings grow with compound interest — set goals, compare strategies, and optimize your plan.
Formula**:
$$A = P \left(1 + \frac{r}{n}\right)^{nt} + PMT \times \frac{\left(1 + \frac{r}{n}\right)^{nt} - 1}{\frac{r}{n}}$$
Where: • $P$ = initial lump sum • $PMT$ = monthly contribution • $r$ = annual rate (APY) • $n$ = compounding periods/year • $t$ = years
Example: $5,000 + $200/mo @ 4% APY for 10 yrs → **$37,314** • Contributions: $29,000 • Interest: **$8,314** (29% of total!)
✅ The 10-Year Rule**:
- Start at 25: Save $300/mo @ 7% → **$664,000 at 65**
- Start at 35: Same → **$307,000 at 65** → **$357,000 less** — even with 10 extra years of contributions!
✅ Round-Up Power**:
- $0.75/day round-up → $274/yr
- At 4% APY for 20 yrs → **$8,200** (vs. $5,475 without interest)
📉 Inflation Reality**:
- $10,000 today = $5,100 in 2045 at 3.4% inflation
- Always use **real return** = APY − inflation for long-term goals
| Strategy | 10-Yr Value @ 4% APY |
|---|---|
| $100/mo | $14,725 |
| $300/mo | $44,175 |
| $500/mo + $5K lump | $80,127 |
| $1,000/mo | $147,250 |
📉 U.S. Reality Check**:
- Avg. savings rate: **3.2%** (BEA, Q1 2025)
- HYSA avg. rate: **4.35%** (vs. 0.01% traditional savings)
- 45% can’t cover a $1,000 emergency (Bankrate)
➡️ Goal-Based
“I need $10K in 2 years” → see how much to save monthly.
➡️ Future Value
“What will $200/mo grow to in 10 years?” — includes lump sum.
➡️ Time to Goal
“How long to save $5K at $200/mo?” — with interest.
You’ll get:
- Required monthly contribution
- Final balance and interest earned
- SVG growth curve (principal vs. interest)
Note: APY = Annual Percentage Yield (includes compounding). Inflation-adjusted values use 3.4% (2025 CPI-U).