Savings Calculator
See how a starting balance plus regular monthly deposits grows with compound interest.
Formula and sources updated · Data sources · 1View algorithm, constants and default inputs (JSON)
Breakdown
About this calculator
This scenario compounds the opening balance and fixed monthly deposits at a constant nominal annual rate converted to a monthly rate. Deposits are assumed at month-end. Inflation, taxes, fees and changing returns are not included, so the projection is not a guarantee.
Worked example
calculated with the default values below
Starting balance 1,000 $ · Monthly deposit 200 $ · Annual interest rate 4 % · Number of years 10 years Final balance 30,940.79 $ · Total deposited 25,000.00 $ · Interest earned 5,940.79 $
Method and assumptions
Formula basis and scope
End-of-month deposits use FV = D × ((1 + i)^n - 1) / i, with i = annual percent / 1200 and n = 12 × years; zero rate uses D × n. Existing savings also grow by (1 + i)^n.
Constant nominal rate and equal monthly deposits; excludes taxes, fees and inflation. It is a projection, not a guaranteed return. Fractional month counts are mathematical projections, not an actual payment schedule.
Data sources
Disclaimer
These calculators give estimates for general information only. They are not financial, tax or investment advice and do not take your personal circumstances into account. Before borrowing, investing or filing, confirm the numbers with a qualified adviser in your jurisdiction.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
FV = P0(1 + r)^n + PMT((1 + r)^n - 1) ÷ r; r = i ÷ 1200, n = 12Y
- P0
- Initial deposit
- PMT
- Monthly deposit
- i
- Annual rate (%)
- Y
- Years
- FV
- Final balance
Monthly rate = annual nominal rate÷100÷12; fixed monthly deposits are made at month-end. Inflation, taxes, fees and rate changes are not modeled.
Frequently asked questions
Should I use a nominal or an after-inflation rate?
Use the real rate — the interest after inflation — if the point of the exercise is to know what the money will buy. A five percent account during four percent inflation is barely growing in purchasing power. Projecting nominal balances over thirty years produces an impressive number that is deeply misleading.
Does the result account for tax on the interest?
No. Interest is usually taxable in the year it is earned, and for higher earners the tax can consume a large share of the return. Either enter the post-tax rate, or model the tax as a reduction in the rate you input, particularly over long periods where the compounding of the untaxed return flatters the outcome.