🏦 Finance Guide 5 min read
How to Calculate Deposit Interest
A bank deposit looks simple — you deposit money, earn interest, get it back at maturity. But the actual amount you receive depends on the interest formula, compounding frequency, and whether tax is withheld. This guide walks through everything with real numbers.
Calculate your deposit payout
Enter your principal, rate, term and tax rate to get gross interest, withholding tax, net interest and total payout.
Deposit Interest Calculator →The simple interest formula
Most fixed-term bank deposits (also called term deposits or time deposits) use simple interest, calculated on the original principal only — not on accumulated interest. The formula is straightforward:
Example: 10,000 × 5% × 1 = 500 gross interest
For terms shorter than a year, prorate by the fraction: a 6-month deposit at 5% earns half the annual interest — 250, not 500.
Worked example: step by step
Suppose you deposit 10,000 (any currency) for 12 months at an annual rate of 5%, with a 10% withholding tax on interest.
| Step | Calculation | Result |
|---|---|---|
| 1. Gross interest | 10,000 × 5% × 1 year | 500.00 |
| 2. Withholding tax | 500 × 10% | − 50.00 |
| 3. Net interest | 500 − 50 | 450.00 |
| 4. Total payout at maturity | 10,000 + 450 | 10,450.00 |
Gross interest reference table
The table below shows gross interest (before tax) for different combinations of principal and annual rate over 12 months, using simple interest. Multiply by 0.9 for a 10% tax rate or 0.84 for 16%.
| Principal | 3% rate | 4% rate | 5% rate | 6% rate | 7% rate |
|---|---|---|---|---|---|
| 5,000 | 150 | 200 | 250 | 300 | 350 |
| 10,000 | 300 | 400 | 500 | 600 | 700 |
| 20,000 | 600 | 800 | 1,000 | 1,200 | 1,400 |
| 50,000 | 1,500 | 2,000 | 2,500 | 3,000 | 3,500 |
| 100,000 | 3,000 | 4,000 | 5,000 | 6,000 | 7,000 |
Simple interest vs compound interest
Fixed-term deposits often pay simple interest on the principal only. Savings accounts and reinvestment products typically use compound interest, where earned interest is added back to the principal and itself earns interest in future periods.
| Type | How it works | Best for | 10,000 at 5% over 3 years |
|---|---|---|---|
| Simple interest | Interest calculated on original principal only | Fixed-term deposits | 1,500 total interest |
| Compound (annual) | Interest added to principal each year | Savings accounts, reinvestment | 1,576 total interest |
| Compound (monthly) | Interest added monthly (12×/year) | High-yield savings | 1,614 total interest |
Over short terms (under 2 years), the difference between simple and compound interest is small. Over 10+ years, compounding creates a substantial gap — this is why reinvesting interest significantly improves long-term returns.
Factors that affect your actual payout
A calculator gives a reliable estimate, but your bank contract is the authoritative source. Several factors can cause the actual payout to differ slightly:
- Day-count convention: Banks may use actual/365, actual/360, or 30/360, giving slightly different results for the same nominal rate
- Early withdrawal penalty: Most fixed deposits charge a fee or forfeit interest if broken early
- Compounding frequency: Monthly vs annual compounding changes the effective annual rate
- Tax residency and applicable tax rate: Withholding tax rates vary by country and, in some jurisdictions, by the size of interest income
- Promotional vs standard rate: Introductory rates may apply only for the first period; the renewal rate may differ
- Account fees: Rare on deposits, but some accounts charge maintenance or management fees that reduce net return
Common questions
What is the formula for simple deposit interest?
Simple interest = Principal × Annual rate × Time (in years). For 10,000 at 5% for 1 year: 10,000 × 0.05 × 1 = 500 gross interest.
What is the difference between gross and net interest?
Gross interest is the total amount earned before any deductions. Net interest is what you actually receive after withholding tax or income tax is subtracted. The gap depends on the applicable tax rate in your jurisdiction.
Is compound interest better than simple interest for savers?
Yes, for longer terms. Compound interest earns returns on previously accumulated interest, which creates accelerating growth over time. The advantage becomes significant for terms of 5 years or more.
Why might my actual bank payout differ from this estimate?
Banks use specific day-count conventions, may apply fees, and sometimes use different compounding frequencies to those assumed by a general calculator. Always treat calculator results as useful estimates for comparison and planning — your signed deposit agreement is the definitive source.
Is deposit interest financial advice?
No. A calculator gives a mathematical estimate to help you compare and plan. It does not constitute financial advice. For investment decisions, consult a qualified financial adviser.
Calculate your deposit return
Enter your amount, rate, term and tax rate to see gross interest, net interest and total payout at maturity.
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