How to Use This Calculator
Enter your starting balance (principal), your expected annual interest rate, any monthly amount you plan to add, and how long you'll save. The calculator updates instantly as you type, showing your final balance, total interest earned, and a year-by-year breakdown.
How Savings Compound Interest Works
Every interest period, your bank calculates interest on your entire balance — including interest you've already earned. This creates a snowball effect: a small balance grows slowly at first, then accelerates. The longer your time horizon, the more dramatic the acceleration.
Adding just $300/month to a $5,000 starting balance at 4.5% over 20 years produces over $120,000 — of which roughly $48,000 is pure interest. Without the monthly contributions, you'd have only about $12,400.
Types of Savings Accounts That Compound Interest
| Account Type | Typical APY (2026) | Compounding | FDIC Insured |
|---|---|---|---|
| High-Yield Savings (HYSA) | 4.5–5.2% | Daily | Yes ($250k) |
| Traditional Savings | 0.01–0.5% | Daily/Monthly | Yes |
| Money Market Account | 4.0–5.0% | Daily | Yes |
| 12-Month CD | 4.5–5.3% | Daily | Yes |
| 5-Year CD | 3.8–4.5% | Daily | Yes |
| I Bonds (inflation-linked) | Variable (~3–5%) | Semi-annual | US Treasury |
Tips to Maximize Your Savings Growth
- Start as early as possible. Time is the most powerful variable in the compound interest formula. Every year you delay costs you exponentially more.
- Use a high-yield savings account. Online banks often offer 10–50× the APY of traditional banks at no extra risk (same FDIC coverage).
- Automate monthly transfers. Treat your savings contribution like a bill — automate it so it happens without thinking.
- Reinvest all interest. Don't withdraw interest; let it stay in the account to keep compounding.
- Increase contributions with raises. Even a 1% increase in contributions each year has an outsized effect over a 20-year horizon.
The Effect of Starting Just 5 Years Earlier
Assumes $300/mo at 4.5%, monthly compounding.