About the High Yield Savings Calculator
A high-yield savings account (HYSA) — online-bank accounts paying multiples of the paltry rates found at traditional banks — is where most emergency funds and short-term cash should sit. Same FDIC insurance, a rate that finally keeps some pace with inflation, and instant access.
This tool computes what your cash earns at a given APY over your horizon — and contrasts it with what a legacy 0.01%–0.5% account would have paid. The gap is the annual “wasted interest” simply from holding cash in the wrong place.
The formula behind it
Both accounts compound annually at their APY:
FV HYSA = deposit × (1+APY)^y • FV legacy = deposit × (1+legacy APY)^yInterest earned on each = final − initial. APY is effective (compounding included). For monthly compounding at an equivalent rate, annual and monthly are close enough at these rates; use the CD calculator or compound calculator for precise frequency modeling.
Worked example
Defaults — $15,000 for 2 years in a HYSA at 4.15% APY, versus a 0.10% legacy account:
- HYSA final = $15,000×(1.0415)^2 ≈ $16,270 → interest $1,270.
- Legacy account final = $15,000×(1.001)^2 ≈ $15,030 → interest $30.
Takeaway: The same cash earned $1,240 more in the right account — money that required no effort, only a transfer.
What moves the result
- APY spread — the difference between where cash sits and could sit is the whole game; today’s HYSAs usually pay mid-4%.
- Rate changes — HYSA rates move with Fed policy; unlike a CD, the APY is not locked.
- Repeated withdrawals — HYSA limits on monthly withdrawals in the past; most banks relaxed these, but above 6 tends to attract review.
- Time in market — an unexpected leave of 6 months or more of idle cash means thousands left behind at 4% vs 0.1%.
Practical tips
- Move idle cash you won’t spend this year into a HYSA. The Lazy cost of sitting in an 0.01% account in today’s rate world is large.
- Treat the HYSA APY as variable — budget on a lower rate (3.5%) and treat any upside as a bonus.
- Ladder your cash between the HYSA for flexibility, math: a CD for the portion you are certain not to touch for a term.
- Confirm FDIC insurance for the online bank — most are, but verify the deposit account name is the bank, not a fintech intermediary.
- For UI and mental model accuracy for interest earnings, use the savings and CD calculators when a locked rate matters.
Frequently asked questions
Are HYSAs safe?
Yes, up to FDIC limits ($250,000 per depositor per institution), the same as any savings account — the rate difference does not change insurance coverage.
Why are HYSA rates so much higher than my bank’s?
Online banks have no branch overhead and compete for deposits with rate. Your legacy rate is old product pricing — the spread is your “free money” for switching.
HYSA vs CD — which for an emergency fund?
HYSA: the fund must be withdrawable at a moment’s notice. CDs suit the stable core you will not touch within a defined term.