Understanding your savings projection
The split between contributions and interest shows how much of the projected balance is your own money versus compounding. The balance of the two shifts with time and rate.
| Horizon | Typical pattern at savings-account rates |
|---|---|
| 1–3 years | Contributions dominate; interest is a small share of the balance |
| 5–10 years | Interest becomes a visible share, especially on larger balances |
| 10+ years | Compounding compounds — interest on interest becomes material |
| Any horizon, 0% rate | Balance equals contributions exactly; the formula reduces to P + PMT·n |
- The model assumes a constant rate and end-of-month deposits with monthly compounding. Actual savings rates change with central-bank policy, and banks credit interest on differing schedules.
- Interest on savings is generally taxable as income in most jurisdictions; taxes are not modeled here.
- Inflation is not modeled: at 3% inflation, money loses roughly half its purchasing power in about 23 years. Comparing the interest rate with expected inflation shows whether real value is growing.
What is a savings calculator?
A savings calculator projects how a savings balance grows when regular deposits are combined with compound interest. Compounding means interest is earned not only on deposits but also on previously credited interest, so growth accelerates over time. The calculator models the two standard components: the future value of the initial lump sum, and the future value of the stream of monthly deposits (an annuity).
US banks advertise deposit rates as APY (annual percentage yield), which already includes the effect of compounding within the year; the Truth in Savings Act (Regulation DD) requires APY disclosure precisely so accounts with different compounding frequencies can be compared directly. This calculator compounds monthly, which closely matches how most savings accounts credit interest.
For time horizons of more than a few years, inflation matters: a balance that grows at 4% while prices rise at 3% gains only about 1% of purchasing power per year. Savings accounts suit short-term goals and emergency funds; agencies such as the CFPB note that long-horizon goals are often addressed with investment accounts, which carry market risk but historically higher expected returns.
How to use this savings calculator
- Enter your starting balance (the initial deposit), or zero if starting from scratch.
- Enter the amount you plan to deposit each month.
- Enter the annual interest rate — the APY quoted by your bank is the closest match.
- Enter the number of years you plan to save.
- Read the projected balance, your total contributions, and the interest earned on top of them.
The savings growth formula
The projection adds the future value of the initial deposit, compounded monthly, to the future value of the monthly deposit stream (an ordinary annuity). Here r is the monthly rate (annual rate ÷ 12) and n the number of months.
Worked example: $1,000 initial plus $250 per month at 4% for 5 years (n = 60, r ≈ 0.003333). The lump sum grows to about $1,221; the deposits grow to about $16,575. The projected balance is roughly $17,795 against $16,000 contributed — about $1,795 of interest earned.
Common mistakes
- Comparing accounts by interest rate when one quotes APY and the other a nominal rate — APY is the comparable figure.
- Ignoring inflation on long horizons; nominal growth can mask flat or falling purchasing power.
- Forgetting that promotional teaser rates expire; the projection assumes the rate persists.
- Overlooking account fees or minimum-balance charges, which can offset interest on small balances.
- Leaving a long-horizon goal entirely in a savings account without considering that historically, diversified investments have outpaced deposit rates over long periods (with risk).
الأسئلة الشائعة
How much will I have if I save $250 a month for 5 years?
At a 4% annual rate compounded monthly, $250 per month for 5 years plus a $1,000 starting balance grows to about $17,795. Of that, $16,000 is your own contributions and roughly $1,795 is interest. At 0% the balance would simply be the $16,000 contributed, so the interest rate accounts for the difference.
What is APY and how is it different from the interest rate?
APY (annual percentage yield) is the effective annual rate including compounding, which US banks must disclose under the Truth in Savings Act (Regulation DD). A nominal rate of 3.93% compounded monthly equals an APY of about 4.00%. Because APY already reflects compounding frequency, it is the correct figure for comparing accounts.
How does compound interest work on a savings account?
Compound interest means each period's interest is calculated on the balance including previously credited interest. With monthly compounding, a 4% annual rate credits about 0.333% each month on the running balance. Over time this produces interest on interest: the longer the horizon, the larger the share of the balance that comes from compounding rather than deposits.
Does this calculator account for inflation or taxes?
No. The projection is in nominal terms and pre-tax. Inflation erodes purchasing power — at 3% annual inflation, prices roughly double in 24 years — and interest income is generally taxable. Both effects mean the real, after-tax growth of a savings balance is lower than the nominal projection shown.
Is savings-account money safe?
In the United States, deposits at FDIC-member banks are insured up to $250,000 per depositor, per insured bank, per ownership category; credit union deposits carry equivalent NCUA insurance. Similar deposit-guarantee schemes exist in the UK (FSCS, £85,000) and the EU (€100,000). Amounts above the insured limit are exposed to the institution's credit risk.
المراجع
- Truth in Savings Act (Regulation DD) — APY disclosure requirements. 12 CFR Part 1030.
- Federal Deposit Insurance Corporation (FDIC). Deposit insurance coverage basics. fdic.gov.
- Consumer Financial Protection Bureau (CFPB). Savings accounts and building emergency savings. consumerfinance.gov.
- Federal Reserve Bank of St. Louis. Interest rates and savings data. FRED Economic Data (fred.stlouisfed.org).
- Bodie Z, Kane A, Marcus AJ. Investments (12th ed.). McGraw-Hill, 2021 — time value of money.