HYSA calculator
Enter your deposit, monthly contribution, and APY to see exactly how a high-yield savings account grows — and how much more it earns than the 0.38% national average.
What is a HYSA calculator?
A HYSA calculator projects a high-yield savings balance month by month: each month the balance grows by (1 + APY)^(1/12) and your contribution is added. At 4.30% APY, $10,000 plus $250 a month becomes $29,009 in five years — $4,009 of it interest. The same deposits at the FDIC national average savings rate of 0.38% (July 2026) earn just $332. The gap between those two numbers is the entire case for moving your savings.
Month-by-month growth.
| Period | Deposited | Interest earned | Balance | Interest share |
|---|---|---|---|---|
| Yr 1 · Mo 1 | $10,250 | $35 | $10,285 | 0% |
| Yr 1 · Mo 2 | $10,500 | $71 | $10,571 | 1% |
| Yr 1 · Mo 3 | $10,750 | $108 | $10,858 | 1% |
| Yr 1 · Mo 4 | $11,000 | $147 | $11,147 | 1% |
| Yr 1 · Mo 5 | $11,250 | $186 | $11,436 | 2% |
| Yr 1 · Mo 6 | $11,500 | $226 | $11,726 | 2% |
| Yr 1 · Mo 7 | $11,750 | $267 | $12,017 | 2% |
| Yr 1 · Mo 8 | $12,000 | $309 | $12,309 | 3% |
| Yr 1 · Mo 9 | $12,250 | $353 | $12,603 | 3% |
| Yr 1 · Mo 10 | $12,500 | $397 | $12,897 | 3% |
| Yr 1 · Mo 11 | $12,750 | $442 | $13,192 | 3% |
| Yr 1 · Mo 12 | $13,000 | $489 | $13,489 | 4% |
| Yr 2 · Mo 1 | $13,250 | $536 | $13,786 | 4% |
| Yr 2 · Mo 2 | $13,500 | $585 | $14,085 | 4% |
| Yr 2 · Mo 3 | $13,750 | $634 | $14,384 | 4% |
| Yr 2 · Mo 4 | $14,000 | $685 | $14,685 | 5% |
| Yr 2 · Mo 5 | $14,250 | $736 | $14,986 | 5% |
| Yr 2 · Mo 6 | $14,500 | $789 | $15,289 | 5% |
| Yr 2 · Mo 7 | $14,750 | $843 | $15,593 | 5% |
| Yr 2 · Mo 8 | $15,000 | $897 | $15,897 | 6% |
| Yr 2 · Mo 9 | $15,250 | $953 | $16,203 | 6% |
| Yr 2 · Mo 10 | $15,500 | $1,010 | $16,510 | 6% |
| Yr 2 · Mo 11 | $15,750 | $1,068 | $16,818 | 6% |
| Yr 2 · Mo 12 | $16,000 | $1,127 | $17,127 | 7% |
| Yr 3 · Mo 1 | $16,250 | $1,188 | $17,438 | 7% |
| Yr 3 · Mo 2 | $16,500 | $1,249 | $17,749 | 7% |
| Yr 3 · Mo 3 | $16,750 | $1,311 | $18,061 | 7% |
| Yr 3 · Mo 4 | $17,000 | $1,375 | $18,375 | 7% |
| Yr 3 · Mo 5 | $17,250 | $1,439 | $18,689 | 8% |
| Yr 3 · Mo 6 | $17,500 | $1,505 | $19,005 | 8% |
| Yr 3 · Mo 7 | $17,750 | $1,572 | $19,322 | 8% |
| Yr 3 · Mo 8 | $18,000 | $1,640 | $19,640 | 8% |
| Yr 3 · Mo 9 | $18,250 | $1,709 | $19,959 | 9% |
| Yr 3 · Mo 10 | $18,500 | $1,779 | $20,279 | 9% |
| Yr 3 · Mo 11 | $18,750 | $1,850 | $20,600 | 9% |
| Yr 3 · Mo 12 | $19,000 | $1,923 | $20,923 | 9% |
| Yr 4 · Mo 1 | $19,250 | $1,996 | $21,246 | 9% |
| Yr 4 · Mo 2 | $19,500 | $2,071 | $21,571 | 10% |
| Yr 4 · Mo 3 | $19,750 | $2,147 | $21,897 | 10% |
| Yr 4 · Mo 4 | $20,000 | $2,223 | $22,223 | 10% |
| Yr 4 · Mo 5 | $20,250 | $2,302 | $22,552 | 10% |
| Yr 4 · Mo 6 | $20,500 | $2,381 | $22,881 | 10% |
| Yr 4 · Mo 7 | $20,750 | $2,461 | $23,211 | 11% |
| Yr 4 · Mo 8 | $21,000 | $2,543 | $23,543 | 11% |
| Yr 4 · Mo 9 | $21,250 | $2,626 | $23,876 | 11% |
| Yr 4 · Mo 10 | $21,500 | $2,710 | $24,210 | 11% |
| Yr 4 · Mo 11 | $21,750 | $2,795 | $24,545 | 11% |
| Yr 4 · Mo 12 | $22,000 | $2,881 | $24,881 | 12% |
| Yr 5 · Mo 1 | $22,250 | $2,968 | $25,218 | 12% |
| Yr 5 · Mo 2 | $22,500 | $3,057 | $25,557 | 12% |
| Yr 5 · Mo 3 | $22,750 | $3,147 | $25,897 | 12% |
| Yr 5 · Mo 4 | $23,000 | $3,238 | $26,238 | 12% |
| Yr 5 · Mo 5 | $23,250 | $3,330 | $26,580 | 13% |
| Yr 5 · Mo 6 | $23,500 | $3,423 | $26,923 | 13% |
| Yr 5 · Mo 7 | $23,750 | $3,518 | $27,268 | 13% |
| Yr 5 · Mo 8 | $24,000 | $3,614 | $27,614 | 13% |
| Yr 5 · Mo 9 | $24,250 | $3,711 | $27,961 | 13% |
| Yr 5 · Mo 10 | $24,500 | $3,809 | $28,309 | 13% |
| Yr 5 · Mo 11 | $24,750 | $3,909 | $28,659 | 14% |
| Yr 5 · Mo 12 | $25,000 | $4,009 | $29,009 | 14% |
The monthly math behind an APY.
APY — annual percentage yield — is the rate after compounding, so the honest way to model monthly growth is to take the 12th root: each month your balance multiplies by (1 + APY)^(1/12). At 4.30% APY that's about 0.352% a month, which is why $10,000 earns roughly $35.15 in month one and exactly $430.00 over a full year — landing precisely on the advertised APY, with contributions added at the end of each month on top.
Compounding is what separates an HYSA from a drawer of cash. Deposit $10,000, add $250 a month, and at 4.30% APY you reach $29,009 in five years. Only $25,000 of that is your own money; $4,009 is interest earning interest. Run the identical deposits at the FDIC national average of 0.38% (July 2026) and interest collapses to $332. At a fixed 3.00% CD-style rate you'd earn about $2,738 — better, but a CD can't take monthly deposits the way a savings account can.
The trade-off for that flexibility is rate risk. HYSA rates float with the federal funds rate, so the 4%+ yields of 2024–2026 can fall quickly when the Fed cuts. That's the reason savers pair an HYSA (liquid emergency fund, variable rate) with a CD ladder (locked rates, staggered access) — each covers the other's weakness.
- B
- Ending balance — value after m months of growth and deposits
- P
- Starting deposit — what you open the account with
- C
- Monthly contribution — added at the end of each month
- r
- Monthly rate — (1 + APY)^(1/12) − 1, exact 12th root of the APY
Six ways to actually use these numbers.
Move the emergency fund first.
The gap between 0.38% and 4.30% on a $15,000 emergency fund is roughly $590 a year for the same zero risk. This is the account to move before optimizing anything else.
Chase APY, ignore sign-up gimmicks.
A $100 bonus on a 3% account loses to a plain 4.3% account within a year on balances over $8,000. Compute a full year of interest before switching for a bonus.
Rates are variable — check quarterly.
Banks quietly drop legacy account rates while advertising new ones. Put a quarterly reminder on the calendar to compare your APY against current offers.
Automate the monthly deposit.
The $250/month in the example contributes $15,000 of the $29,009 five-year total. Automation, not the rate, does most of the heavy lifting.
Keep it under $250K per bank.
FDIC insurance caps at $250,000 per depositor per bank. Above that, open a second HYSA elsewhere — rates barely differ at the top of the market.
Budget for the tax bill.
Interest is ordinary income. Earning $430 in the 22% bracket nets about $335. High earners in taxed states may prefer Treasury bills, which are state-tax exempt.