GrowthCalc › Daily Compound Interest Calculator
Daily Compound Interest Calculator: how it works
Banks like to advertise daily compounding because it sounds like more interest, and technically it is. The question is how much more. For a savings account at 4.5 percent, the difference between daily and monthly compounding on $20,000 over five years is a few dollars. The difference between 4.5 percent and 4.0 percent is a few hundred.
The preset sets GrowthCalc to daily compounding at 4.5 percent on a $20,000 balance with $250 added monthly over five years, a typical high-yield savings setup. Change the frequency select to monthly or annually and watch the final balance; the gap is smaller than most people expect.
How daily compounding is calculated
With daily compounding, the bank divides the annual rate by 365, applies that fraction every day, and the next day's interest is calculated on the slightly larger balance. The effective annual yield (APY) is (1 + r/365)365 − 1. At a 4.5 percent nominal rate that is 4.60 percent APY; monthly compounding gives 4.59 percent; annual compounding gives exactly 4.50 percent. GrowthCalc simulates month by month using the effective monthly rate for the frequency you choose, so contributions are added every month regardless of how often interest is credited.
- Compare APY, not nominal rates, when choosing an account.
- A rate 0.25 points higher beats any compounding frequency advantage.
- Interest is typically taxable in the year it is credited.
When frequency does matter
Compounding frequency becomes meaningful when rates are high or balances are large: on $500,000 at 8 percent, daily versus annual compounding differs by about $1,600 a year. It also matters in reverse on debt. Credit cards usually compound daily, which is part of why balances grow faster than the headline APR suggests; the same calculator logic applies, just with you on the wrong side of it.
For most savers the practical advice is simple: pick the highest APY with no fees, automate contributions, and let time do the compounding. Not financial advice; rates shown are examples, not offers.
Frequently asked questions
Is daily compounding better than monthly?
Slightly. At typical savings rates the difference is a few hundredths of a percent in APY, which on a $20,000 balance is a few dollars a year.
How do I convert a nominal rate to APY?
APY = (1 + r/n)^n − 1, where n is the number of compounding periods per year. Enter the nominal rate here and pick the frequency; the final balance reflects the APY.
Does the calculator compound contributions daily too?
Contributions are added monthly and then earn interest at the chosen frequency from that point on, which matches how most accounts work.
Can I see the difference between frequencies side by side?
Yes with GrowthCalc Pro: save the daily version as a scenario, switch to annual, and compare both on the chart and in the table.
Looking for the full guide, tips and the complete FAQ? Read the main GrowthCalc page.