Add-On CD Calculator
Add-on CDs let you keep depositing during the term instead of locking in one lump sum. Enter the opening deposit, monthly additions, APY, and term to see what the account is worth at maturity.
Estimates only — not financial advice. This calculator gives approximate figures for planning. It is not financial, tax, or legal advice; check with a qualified professional before making decisions.
How the add-on CD calculator works
A regular CD freezes your deposit on day one; an add-on CD lets you feed it with new deposits while the guaranteed rate keeps working. This calculator compounds the opening deposit for the full term, then grows each monthly addition for the months remaining when it lands — the standard future-value-of-an-annuity math — and adds the two together.
That steady feeding matters more than most savers expect: a $1,000 opener with $200 monthly additions at 4.25% APY for 24 months puts in $5,800 total and earns interest on money that arrives early, finishing well above a plain savings account at the same rate.
FV = P(1+r)n + PMT × ((1+r)n−1)/r · additions assumed at month end
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Add-on CD calculator FAQ
What is an add-on CD?
A certificate of deposit that lets you make additional deposits during the term at the original guaranteed rate — unlike a regular CD, which locks your deposit amount on day one.
How is an add-on CD different from a regular CD?
The rate guarantee works the same, but you can keep feeding an add-on CD with new deposits. Regular CDs accept only the opening deposit; adding more means opening a second CD at the current rate.
Are add-on CD rates lower than regular CD rates?
Often slightly, yes — banks price in the flexibility. But a slightly lower rate that you can keep feeding usually beats a higher rate on a one-time deposit.
Can I withdraw my additions before maturity?
Generally no without an early-withdrawal penalty, just like the opening deposit. Add-on refers to deposits, not withdrawals — plan on leaving the money alone until maturity.
Is the interest compounded monthly?
Most add-on CDs compound daily or monthly and credit the stated APY. This calculator compounds monthly at APY ÷ 12, which matches how APY is defined.