Monthly savings math
The core formula is the future value of a series of monthly deposits plus your starting balance compounding:
FV = P·(1+i)ⁿ + M·((1+i)ⁿ − 1)/i
where P = starting amount, M = monthly deposit, i = monthly rate (annual ÷ 12), n = months. The calculator solves for either n (given a monthly amount) or M (given a deadline).
Getting the most from the math
- High-yield savings (3.5–5% in recent years) beats a checking account — the interest on a 5-year, $300/month plan can be $1,000+.
- Automate it: a standing transfer on payday turns "saving" into "never seeing the money".
- Emergency fund first: most advisors suggest 3–6 months of expenses before longer-term goals.
- Rate is an assumption: APY changes; the calculator uses it as a constant for planning, not a promise.