How to use it 01 Enter principal, annual rate, years and compounds per year. 02 Add a monthly contribution if the plan saves regularly. 03 Read future value, total interest, total contributed and the EAR. 04 Type a target future value and press the goal button to solve the monthly contribution that reaches it. Worked readouts 5,000 at 6% for 8 years. Compounded 12 times a year → 8,070.71 , of which 3,070.71 is interest; compounded once a year → 7,969.24 , a gap of 101.47 . Adding 300 a month at the monthly frequency → 44,919.28 from 33,800 contributed, so 11,119.28 of the balance is interest. A 100,000 target over the same 8 years asks for 748.44 a month. A 1,000 principal at 5% for 1.7 years compounds over the fractional 1.7 periods (P × (1 + r)^1.7) → 1,086.48 ; pro-rating a whole period plus 0.7 instead would give 1,086.75.
Compounding versus contributing Without contributions the balance is P × (1 + r/n)^(n·t) for rate r, frequency n and t years; the panel also runs the period-by-period loop so a contribution can be added each period. The EAR is (1 + r/n)^n − 1: 6% compounded monthly is 6.1678% , not 6%.
Limits
Nominal rates only. The rate you type is nominal and divided by the compounding frequency; the panel quotes no rate and fetches no market data.
No taxes or inflation. The balance is gross and nominal; a real return needs your own adjustment. What it does not do. It does not solve for the rate or the term — use TVM — and it does not price loan repayment; Loan does that. This page provides general information and scenario estimates based only on the inputs you provide. It is not investment, tax, legal, or other professional advice and does not recommend any rate, product, or institution. The contribution timing is the trap Contributions enter at period end, so with annual compounding a year of 300-a-month contributions is one 3,600 deposit at year end that earns nothing in that year, while monthly compounding credits each 300 at its own period end. Switching frequency changes both the interest and the contribution schedule, which is why the panel shows total contributed separately. The frequency also moves the EAR: 6% is 6.1678% compounded monthly but 6.0000% compounded annually.
Where it is used Projecting a regular savings plan Compare the same monthly amount at 1 and 12 compounds a year; the difference is the frequency effect, not a rate change.
Finding the monthly amount for a target Enter the target and solve the contribution, then check total contributed against future value to see the interest share.
Privacy All inputs and readouts stay in the browser; nothing is uploaded or stored.
References
Wikipedia, Compound interest , en.wikipedia.org （访问日期：2026-10-07）— compounding frequencies and growth.
Wikipedia, Effective interest rate , en.wikipedia.org （访问日期：2026-10-07）— the EAR formula and the nominal-to-effective gap.
Wikipedia, Time value of money , en.wikipedia.org （访问日期：2026-10-07）— present and future value.
OpenStax, Principles of Finance , openstax.org （访问日期：2026-10-07）— savings and compounding examples.
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Reviewed by CalcX Editorial Team
Updated 2026-10-07