Savings Calculator - Compound Interest with Contributions
Savings Calculator
A savings calculator shows how regular contributions, combined with compound interest, can grow into significant wealth over time. The key variables are how much you save, the interest rate, and how long you save - time is often the most powerful factor.
Conversion Formula
FV = P(1+r)^n for the initial deposit, plus C × [(1+r)^n - 1] / r for regular contributions. P is the initial deposit, r is the rate per period, n is total periods, and C is the contribution per period (monthly converted to match compounding frequency).
Step-by-Step Examples
$5,000 start, $200/mo, 4.5%, 10 years, monthly = $36,153.72 final balance
Contributions: $29,000; Interest earned: $7,153.72
$1,000 start, $500/mo, 7%, 20 years, monthly = $260,775.23 final balance
Contributions: $121,000; Interest: $139,775.23
$10,000 start, $0/mo, 5%, 30 years, annually = $43,219.42 final balance
Initial only; compound growth over 30 years
History
Compound interest was described by Albert Einstein as "the eighth wonder of the world." The concept dates back to Babylonian mathematics, but its systematic application in banking became widespread in 17th-century Europe.
Common Use Cases
- Emergency fund planning
- Saving for a house down payment
- College savings estimation
- Setting savings goals with a deadline
Frequently Asked Questions
How does compound interest work on savings?
Compound interest earns interest on your interest. Each period, your interest is added to the balance and the next period's interest is calculated on the new higher balance. Over time this creates exponential growth - dramatically more than simple interest.
Does contribution timing matter?
Yes. Contributions made at the beginning of the period (annuity due) earn slightly more than contributions at the end (ordinary annuity). This calculator assumes end-of-period contributions, which is the more conservative estimate.
What is a realistic savings rate?
High-yield savings accounts currently offer 4-5%. Money market funds range 3-5%. Conservative bond portfolios average 3-5%. Stock-heavy portfolios have historically averaged 7-10% before inflation. The rate you should use depends on where your money is invested.
What is the Rule of 72 for savings?
Divide 72 by your annual interest rate to estimate how many years until your savings double. At 4%, money doubles in about 18 years (72/4). At 8%, it doubles in 9 years (72/8).