Regular Savings Interest Calculator

Before you calculate

Use this calculator when you want a focused regular-savings estimate with the same deposit every month and no tax, fee, withdrawal, inflation, or changing-rate model. Use the broader savings calculator when deposits can grow or tax-rate assumptions matter, and use the interest calculator when contribution timing or compounding frequency needs more control.

Formula summary

The calculator converts the annual percentage input to a monthly decimal rate by dividing by 100 and 12. It grows the starting balance for every month, adds fixed monthly deposits as end-of-month deposits, uses a zero-rate branch when the rate is 0, then reports final balance, total deposits, and interest earned before tax, fees, withdrawals, or product rules.

Worked example

Example: $5,000 plus $250 monthly at 4.25 percent for 60 months

With the default inputs, a $5,000 starting balance, $250 added at the end of each month, a 4.25 percent annual rate assumption, and 60 months produce a final balance of $22,861.64. Total deposits are $20,000.00, so the model shows $2,861.64 of gross interest before tax, fees, withdrawals, changing rates, or provider rules. A zero-rate check with $1,250, $400 monthly, and 24 months produces $10,850.00 final balance and $0.00 interest.

The result is useful for explaining the fixed monthly-deposit model. It is not a savings-account quote, APY/AER disclosure, tax calculation, provider comparison, or recommendation about where to save.

Assumptions

• The starting balance, monthly deposit, annual rate, and term in months stay fixed for the whole projection.
• Monthly deposits are modeled at month end. The calculator does not model beginning-of-month deposits, skipped deposits, deposit caps, withdrawals, rate changes, fees, bonus rates, inflation, provider rules, or live savings products.
• Results use the numbers entered on the page, round currency outputs to two decimals, and are educational gross estimates rather than financial, tax, legal, lending, investment, provider, or regulated advice.

Common mistakes to avoid

• Treating the entered annual rate as a real APY, AER, product quote, or bank-rate promise. The calculator only uses the rate you enter as a planning assumption.
• Comparing regular saver accounts without checking deposit limits, withdrawal rules, variable-rate terms, bonus-rate conditions, tax treatment, and whether the provider displays gross rate, AER, or APY.
• Expecting tax or account-wrapper treatment in the result. US labels are before federal or state tax, and UK labels are before Personal Savings Allowance, ISA, or other tax treatment.

Methodology and sources

This calculator is an original implementation based on documented formulas, app-specific assumptions, deterministic fixtures, edge cases, rounding policy tests, and internal validation. It is not copied from a single source.

Outputs are checked with deterministic fixtures, edge cases, rounding policy tests, and internal independent comparator checks where overlapping outputs are available. The result remains an educational estimate, not a quote, approval, tax answer, or personalised advice.

Formula version 2026.05.20-us-uk-gross-savings. The version marks the calculation logic and validation fixture set used for this estimate.

• CFPB Regulation DD Appendix A should be used before copy discusses US annual percentage yield disclosure calculations, advertised APY terminology, account-disclosure assumptions, bonuses, fees, or product-specific yield claims.
• IRS Topic 403 and relevant state tax-authority materials should be used before copy discusses US taxable interest, reporting, withholding, tax-exempt interest, state tax, or personal tax outcomes.
• GOV.UK Tax on savings interest, HMRC materials, and relevant UK tax guidance should be used before copy discusses Personal Savings Allowance, starting rate for savings, ISA treatment, joint-account interest, foreign savings, or UK tax payment rules.
• FCA, MoneyHelper, provider disclosures, FDIC, FSCS, bank terms, and relevant local regulators should be used before copy discusses AER, gross or net savings rates, variable rates, promotional rates, account protection, eligibility, withdrawal limits, deposit caps, provider comparisons, or jurisdiction-specific product claims.

Estimate only

The result is educational and is not financial, tax, legal, lending, investment, or regulated advice. Real provider terms, fees, rates, taxes, and personal circumstances can change the final answer.

Formula and help: read the full regular savings interest calculator methodology notes.

Related reading

• How Calcs.finance validates calculator formulas
• Estimate limitations and not-advice disclaimer

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