# Simple interest calculator

> Calculate simple interest (I = P × r × t) and the maturity amount on a principal for a term in years, months or days.

Versione interattiva: https://www.calcopenly.com/it/finance/simple-interest-calculator
Argomento: Calcolatori finanziari

Simple interest is paid only on the original principal: I = P × r × t, where r is the yearly rate as a decimal and t the time in years. A term in months is divided by 12, and a term in days by 365 (actual/365) or by 360, the banker's year some lenders and money markets use. The amount due at maturity is A = P(1 + rt).

With the defaults, 10,000 at 6% for 3 years earns 600 a year and 1,800 in total, for a maturity amount of 11,800. Compounded yearly at the same rate, the same deposit would reach 11,910.16, which is 110.16 more.

Interest here never earns interest of its own. Savings accounts and most deposits compound, so use the compound interest calculator for them; simple interest suits short loans, flat-rate quotes and interest accrued between coupon dates.

## Dati

- **Capitale**
- **Interest rate (per year)**
- **Tempo**
- **Time in** (opzioni: Anni, Mesi, Days)
- **Days in a year** (opzioni: 365 (actual/365), 360 (banker's year))

## Risultati

- Interessi — risultato principale
- Total amount
- Interest per year
- Amount if compounded yearly

## Formula

$$
I = P \cdot r \cdot t,\qquad A = P(1 + r t)
$$

## Esempi svolti

### 10,000 at 6% for 3 years

- Capitale: 10,000
- Interest rate (per year): 6%
- Tempo: 3
- Time in: Anni
- **Interessi: 1,800.00**
- **Total amount: 11,800.00**
- **Amount if compounded yearly: 11,910.16**
- Fonte di verifica: 10000 × 0.06 × 3 by hand; 10000 × 1.06³ = 11910.16 (Python decimal)

### 5,000 at 8% for 9 months

- Capitale: 5000
- Interest rate (per year): 8%
- Tempo: 9
- Time in: Mesi
- **Interessi: 300.00**
- **Total amount: 5,300.00**
- Fonte di verifica: 5000 × 0.08 × 9/12 by hand

### 20,000 at 7.5% for 90 days, actual/365

- Capitale: 20,000
- Interest rate (per year): 7.5%
- Tempo: 90
- Time in: Days
- Days in a year: 365 (actual/365)
- **Interessi: 369.86**
- Fonte di verifica: 20000 × 0.075 × 90/365 = 369.8630… (Python decimal)

### Same loan on a 360-day year

- Capitale: 20,000
- Interest rate (per year): 7.5%
- Tempo: 90
- Time in: Days
- Days in a year: 360 (banker's year)
- **Interessi: 375.00**
- Fonte di verifica: 20000 × 0.075 × 90/360 by hand

### Zero rate

- Capitale: 1000
- Interest rate (per year): 0%
- Tempo: 5
- Time in: Anni
- **Interessi: 0.00**
- **Total amount: 1,000.00**
- Fonte di verifica: Definition: no rate, no interest

## Domande

### How do you calculate simple interest?

Multiply the principal by the yearly rate and by the time in years: I = P × r × t. 10,000 at 6% for 3 years earns 10,000 × 0.06 × 3 = 1,800, so 11,800 is repaid. For a term in months, divide by 12 first: 5,000 at 8% for 9 months earns 5,000 × 0.08 × 9/12 = 300.

### How do you calculate simple interest for a number of days?

Divide the days by the day-count basis before multiplying. 20,000 at 7.5% for 90 days earns 20,000 × 0.075 × 90/365 = 369.86 on an actual/365 basis, and 375.00 on a 360-day banker's year. Excel's ACCRINTM function uses basis 3 for actual/365 and basis 2 for actual/360.

### How do you find the rate or the time from simple interest?

Rearrange I = P × r × t. The rate is r = I ÷ (P × t): earning 1,800 on 10,000 over 3 years means 1,800 ÷ 30,000 = 6% a year. The time is t = I ÷ (P × r): earning 3,000 on 10,000 at 6% takes 3,000 ÷ 600 = 5 years.

### Is simple interest better than compound interest?

For a borrower, yes; for a saver, no. Simple interest grows in a straight line, while compound interest also earns interest on interest. On 10,000 at 6%, the gap is only 110.16 after 3 years (1,800 against 1,910.16), but after 20 years simple interest totals 12,000 while yearly compounding adds 22,071.35.

### Quanto è preciso «Simple interest calculator»?

La precisione dipende dai dati inseriti e dalle ipotesi del metodo. Il calcolo decimale usa 50 cifre significative, ma stime, metodi numerici e dati di origine possono essere meno precisi; l’arrotondamento visualizzato non elimina questi limiti. Esempi svolti verificati con fonti indipendenti: 5. Per esempio, «10,000 at 6% for 3 years» viene verificato con 10000 × 0.06 × 3 by hand; 10000 × 1.06³ = 11910.16 (Python decimal).

### Da dove proviene il metodo?

OpenStax Prealgebra 2e — Simple Interest Applications (I = Prt); Brealey, Myers & Allen — Principles of Corporate Finance, ch. 2 (simple vs compound interest); Microsoft Excel ACCRINTM function (simple interest accrued to maturity, basis 2 = actual/360, 3 = actual/365).

## Fonti

- [OpenStax Prealgebra 2e — Simple Interest Applications (I = Prt)](https://openstax.org/books/prealgebra-2e/pages/6-4-solve-simple-interest-applications)
- Brealey, Myers & Allen — Principles of Corporate Finance, ch. 2 (simple vs compound interest)
- [Microsoft Excel ACCRINTM function (simple interest accrued to maturity, basis 2 = actual/360, 3 = actual/365)](https://support.microsoft.com/en-gb/office/accrintm-function-f62f01f9-5754-4cc4-805b-0e70199328a7)

_Solo per pianificare. Finanziatori, autorità fiscali e mercati applicano propri arrotondamenti, costi e regole; conferma le cifre con loro prima di assumere impegni._