Find the interest and final balance when interest never compounds
Enter a valid principal
Enter a valid rate (0-100)
Enter valid years (0-100)
Enter valid months (0-11)
Simple interest is the most basic way money grows or debt accrues: interest is charged on the original principal and on nothing else. No matter how many years pass, the interest added each year is the same, because the amount it is calculated from never changes.
Enter a principal, an annual rate and a term in years plus months, and the tool returns the interest earned and the final balance. It also shows the interest generated per year and what share of the final balance is interest, so you can see at a glance how the money splits.
P is the principal, r the annual rate as a decimal (5% becomes 0.05) and t the time in years. The term must be in years — that is why the calculator converts the months you enter into a fraction: 3 years 6 months becomes t = 3.5.
Suppose you lend $10,000 at 5% a year for 3 years and 6 months. The interest is 10,000 × 0.05 × 3.5 = $1,750, so the final balance is $11,750. Each year contributes the same $500, and the extra half year contributes $250. Had the same money compounded annually instead, the balance after 3.5 years would be about $11,842 — roughly $92 more, because interest would earn interest.
| Term | Interest (simple) | Balance |
|---|---|---|
| 1 year | $500.00 | $10,500.00 |
| 3 years | $1,500.00 | $11,500.00 |
| 3 years 6 months | $1,750.00 | $11,750.00 |
The most common mistakes are mixing up months and years, entering the rate as 5 instead of 0.05 when computing by hand, and assuming simple interest when a contract actually compounds. The second line of the formula always wins in the long run: given the same rate, compound interest is never less than simple interest over any term beyond the first period.
单利是资金增值或债务累积最基础的方式：利息只按原始本金计算，其他一概不算。无论经过多少年，每年新产生的利息都一样多，因为它的计算基数从不改变。
输入本金、年利率以及「年 + 月」形式的期限，工具会给出利息收益与期末总额，同时展示每年产生的利息、利息占期末总额的比例，让你一眼看清资金的构成。
公式里的时间必须以「年」为单位——这正是计算器把你输入的月数换算成小数的原因：3 年 6 个月对应 t = 3.5。利率则要写成小数形式，5% 即 0.05。
假设你按年利率 5% 借出 10,000 元，期限 3 年 6 个月：利息 = 10,000 × 0.05 × 3.5 = 1,750 元，期末总额 11,750 元。每年贡献 500 元，多出的半年再贡献 250 元。如果同样的钱改为按年复利，3.5 年后约为 11,842 元——多出约 92 元，因为复利让利息也生息。
| 期限 | 单利利息 | 期末总额 |
|---|---|---|
| 1 年 | 500.00 元 | 10,500.00 元 |
| 3 年 | 1,500.00 元 | 11,500.00 元 |
| 3 年 6 个月 | 1,750.00 元 | 11,750.00 元 |
最常见的错误是把月数当年数用、手算时忘记把 5% 换成 0.05，以及合同实际按复利计息却误以为单利。长期来看，第二条公式永远占上风：只要超过第一期，同样利率下复利收益绝不会低于单利。
Simple interest is interest charged only on the original principal. It never compounds, so the same amount of interest is added every year: Interest = Principal × Rate × Time.
Compound interest is added back to the balance and earns interest itself. $10,000 at 5% for 3 years earns $1,500 in simple interest but about $1,576 compounded annually — the gap widens every year.
Many auto loans, short-term personal loans, bonds and coupons use simple interest. If a loan says interest accrues daily on the principal only and payments cover interest first, it is a simple-interest loan.
Last reviewed: October 5, 2026 · How we calculate · Sources: Investor.gov, CFPB, Federal Reserve
最近复核：2026 年 10 月 5 日 · 我们的计算方法 · 来源：Investor.gov、CFPB、美联储