Interest earned is not the same as the ending balance
To estimate savings interest, first distinguish money supplied from money earned. With no withdrawals, modeled interest equals ending balance minus opening savings minus new deposits. A balance that grows quickly through regular contributions does not mean the account earned that entire increase as interest. Keep all three quantities visible before interpreting a projection or comparing accounts.
This guide uses invented constant yields and regular deposits to explain the reconciliation. It does not quote current rates, recommend a bank or guarantee earnings. An actual account can use changing rates, daily balances, tiers, fees or restrictions. The model is useful when those assumptions are stated, not when its smooth growth is presented as an exact future statement.
Begin with an untouched opening amount
For a hypothetical $3,000 opening amount and 4 percent effective annual yield, one year with no additions or withdrawals gives $3,000 × 1.04 = $3,120. Interest is $120. If the same constant effective yield applies for five years and all interest remains in the account, balance is $3,000 × 1.04^5, approximately $3,649.96, and interest is about $649.96.
The five-year earnings exceed five times $120 because earlier interest participates in later growth. That does not establish that a provider will maintain 4 percent for five years. The effective annual yield is a scenario input. A guarantee, promotional period or variable-rate condition must come from the actual account terms rather than from the mathematical exponent.
Add deposits at the time they actually enter the model
Now keep the $3,000 opening savings but add $200 at each month end for twelve months. Convert 4 percent effective annual yield to i = 1.04^(1/12) − 1. The ending-balance formula is $3,000 × (1 + i)^12 + $200 × [(1 + i)^12 − 1]/i. It gives approximately $5,563.69.
Total money supplied is $3,000 + twelve deposits of $200 = $5,400. Subtracting that contribution total leaves about $163.69 of modeled interest. Subtracting only the opening $3,000 would report $2,563.69 and incorrectly count the $2,400 of additional deposits as earnings. This distinction is essential when reviewing any savings account with ongoing transfers.
See why depositing all the money upfront gives another answer
If the full $5,400 were available and deposited at the start, 4 percent effective annual growth for one year would produce $5,616 and $216 interest. That differs from the monthly-deposit example because money arriving later had less time in the account. It is not evidence that the monthly formula is missing interest; the cash availability and timing changed.
Likewise, moving each monthly contribution to the beginning of its month gives that contribution one extra period of growth under the model. Compare schedules with the same deposit count and state their timing. Do not assume a future paycheck was available on day one when comparing with an upfront deposit that the saver could not actually make.
Keep the rate definition consistent with the account question
An effective annual yield already expresses the annual compounding effect under its stated conditions. For a monthly equivalent-rate illustration, use a twelfth root of its growth factor. A nominal annual interest rate divided by twelve is a different input convention. The same displayed percentage can therefore lead to different modeled earnings if the meaning of the rate is changed silently.
The Savings Calculator uses effective annual yield, while the Compound Interest Calculator uses nominal annual rate and selected compounding frequency. Read the field labels rather than copying a percentage between tools without conversion. Neither tool retrieves live account rates or determines whether a promotional yield applies to the entire balance and full selected horizon.
Use the Savings Calculator's goal-based output correctly
The current Savings Calculator solves for a monthly contribution to reach a goal; it is not a fixed-deposit forward earnings interface. For example, with $3,000 initial savings, a $6,000 target, twelve months, 4 percent effective annual yield and end-month deposits, it returns $235.71 monthly after upward cent rounding. Total contributed is $5,828.52.
The projected ending balance is about $6,000.01, making interest about $171.49. The small target excess comes from rounding the required deposit upward. These earnings belong to that $235.71 contribution plan, not to the earlier $200 plan. If your question fixes monthly deposits instead, use an appropriate separate forward worksheet rather than misreading a target solver's result.
Account for withdrawals, charges and actual observations separately
For a reconciled account record with withdrawals, the identity becomes ending balance + money withdrawn − opening balance − new deposits. The residual reflects net growth and any unseparated charges, not necessarily gross interest alone. If the statement lists fees separately, retain them so that net earnings and interest credited do not acquire the same label by accident.
Taxes, account conditions and access restrictions can also affect a real outcome, and this guide does not calculate them. Do not treat an assumed effective yield as evidence that an account has no fees or that every deposited dollar qualifies for a special rate. Reproduce actual earnings from the provider's transactions and terms where an exact statement check is needed.
Review scenarios without mistaking them for a quote
Keep opening money, deposit amounts and dates, rate convention, horizon and exclusions in the record. Test zero yield as a reconciliation check: with the $3,000 opening amount and twelve $200 deposits, balance is $5,400 and interest is zero. A nonzero earnings result in that zero-yield setup indicates a labeling or formula problem rather than a surprisingly generous account.
This article is educational and is not savings-product, financial or tax advice. An estimate can show how earnings respond to a chosen yield and funding plan, but cannot ensure the rate persists or decide which account suits a person. The useful answer is a separately labeled interest figure supported by the complete contribution timeline, not a large ending balance called profit.