Why does beginning contribution timing produce a larger balance?

Each beginning-of-period contribution earns interest for one additional compounding period.

Which inputs does Compound interest calculator use?

It uses the visible fields Starting principal, Annual interest rate, Term in years, Compounding frequency, Contribution each compounding period, Contribution timing. No hidden value is substituted for an omitted required input.

What happens when Compound interest calculator receives an invalid or extreme value?

The page rejects missing, ambiguous, out-of-range, or non-finite values and refuses to display a non-finite result.

Why can Compound interest calculator differ from another result?

Different unit conventions, endpoint policies, fee or rate assumptions, formula domains, and premature rounding can produce a different answer.

Can I use Compound interest calculator as professional advice?

No. It is an educational estimate, not financial, tax, investment, accounting, or lender advice.

How can I verify the Compound interest calculator result?

Recalculate the two evaluated examples without rounding intermediate values and compare the declared formula or convention with Investor.gov compound interest formula.

Compound interest calculator

Compound growth planner

Model an initial amount and regular contributions with an explicit compounding frequency and contribution timing.

Estimated result

Projected balance16,470.09

Initial amount10,000.00

Total contributions0.00

Modeled growth6,470.09

Progress chart

Model an initial amount and regular contributions with an explicit compounding frequency and contribution timing.

Projected balanceTotal contributions

Complete schedule

Elapsed years	Initial amount	Modeled growth	Projected balance
1	10,000.00	511.62	10,511.62
2	10,000.00	1,049.41	11,049.41
3	10,000.00	1,614.72	11,614.72
4	10,000.00	2,208.95	12,208.95
5	10,000.00	2,833.59	12,833.59
6	10,000.00	3,490.18	13,490.18
7	10,000.00	4,180.36	14,180.36
8	10,000.00	4,905.85	14,905.85
9	10,000.00	5,668.47	15,668.47
10	10,000.00	6,470.09	16,470.09

Formula

Compound interest calculator evaluates the registered expression “r=x₂/100; i=r/x₄; N=x₃x₄; τ=τ(x₆)∈{1;1+i}; A=x₁(1+i)^N+x₅·{N:i=0;((1+i)^N−1)τ/i:i≠0}; x₁=Starting principal; x₂=Annual interest rate; x₃=Term in years; x₄=Compounding frequency; x₅=Contribution each compounding period; x₆=Contribution timing” with the validated inputs. Full calculation precision is retained until the result is formatted for display.

r=x₂/100; i=r/x₄; N=x₃x₄; τ=τ(x₆)∈{1;1+i}; A=x₁(1+i)^N+x₅·{N:i=0;((1+i)^N−1)τ/i:i≠0}; x₁=Starting principal; x₂=Annual interest rate; x₃=Term in years; x₄=Compounding frequency; x₅=Contribution each compounding period; x₆=Contribution timing

Investor.gov compound interest formula

What this calculator answers

Project future value from a starting principal plus equal contributions made once per selected compounding period, including beginning-versus-end timing.

Variables, defaults, and limits

Starting principal: Starting principal is a number input. The displayed starter value is 10,000; it is an example, not a hidden assumption.; Default: 10,000; Accepted values: Minimum: 0. Numeric entries must be finite and unambiguous.
Annual interest rate: Annual interest rate is a number input. The displayed starter value is 5; it is an example, not a hidden assumption.; Default: 5; Accepted values: Allowed range: -99.99 to 1,000. Numeric entries must be finite and unambiguous.
Term in years: Term in years is a number input. The displayed starter value is 10; it is an example, not a hidden assumption.; Default: 10; Accepted values: Allowed range: 0 to 100. Numeric entries must be finite and unambiguous.
Compounding frequency: Compounding frequency is a choice input. The displayed starter value is 12; it is an example, not a hidden assumption.; Default: 12; Accepted values: The field has no narrower HTML limit, but it must still satisfy the documented formula domain and produce a finite result. Available choices: 1, 2, 4, 12, 365.
Contribution each compounding period: Contribution each compounding period is a number input. The displayed starter value is 0; it is an example, not a hidden assumption.; Default: 0; Accepted values: Minimum: 0. Numeric entries must be finite and unambiguous.
Contribution timing: Contribution timing is a choice input. The displayed starter value is End of period; it is an example, not a hidden assumption.; Default: End of period; Accepted values: The field has no narrower HTML limit, but it must still satisfy the documented formula domain and produce a finite result. Available choices: End of period, Beginning of period.

Formula and calculation rule

r=x₂/100; i=r/x₄; N=x₃x₄; τ=τ(x₆)∈{1;1+i}; A=x₁(1+i)^N+x₅·{N:i=0;((1+i)^N−1)τ/i:i≠0}; x₁=Starting principal; x₂=Annual interest rate; x₃=Term in years; x₄=Compounding frequency; x₅=Contribution each compounding period; x₆=Contribution timing

Worked examples