Pro Rata Calculator – Prorated Amounts for Partial Periods

The formula is straightforward: Prorated Amount = Total Amount × (Partial Days ÷ Full Period Days). First, determine the daily rate by dividing the total amount by the number of days in the full period. Then multiply that daily rate by the number of days actually used or needed. This method works for any time period — days, weeks, months, or years.

Common use cases include: rent payments when moving in or out mid-month, subscription services when starting or canceling partway through a billing cycle, employee salaries for partial months of work, insurance premiums for partial coverage periods, utility bills for partial billing cycles, and freelance contracts with partial service periods.

Prorated rent is calculated by dividing the monthly rent by the number of days in that month, then multiplying by the number of days you'll occupy the property. Example: If rent is $1,500/month and you move in on the 12th of a 30-day month, you'd pay for 19 days: $1,500 ÷ 30 × 19 = $950.00. Always confirm with your landlord whether they use a 30-day standard or the actual days in that specific month.

For annual subscriptions, the total annual fee is divided by 365 days (or 366 for leap years) to get a daily rate, then multiplied by the number of days used. Example: A $120 annual subscription canceled after 45 days: $120 ÷ 365 × 45 = $14.79. Many SaaS companies use this method for refunds or upgrade/downgrade adjustments.

Per diem specifically means "per day" and refers to a fixed daily rate (like a $50/day travel allowance). Pro rata is broader — it means any proportional allocation, whether based on days, months, usage, or any other measurable unit. Per diem is essentially a type of pro rata calculation where the unit is always one day.

For a partial month salary, divide the monthly salary by the total working days in that month (or calendar days, depending on company policy), then multiply by the days actually worked. Example: $5,000 monthly salary, 22 working days in the month, employee works 10 days: $5,000 ÷ 22 × 10 = $2,272.73. Some employers use calendar days (30 or 31) instead of working days — check your employment contract.

Yes, absolutely. Pro rata calculations work perfectly for partial years. Divide the annual amount by 365 (or 366 for leap years) to get the daily rate, then multiply by the days needed. For even simpler math with full months, divide the annual amount by 12 and multiply by the number of months. Example: $2,400 annual insurance for 3 months: $2,400 ÷ 12 × 3 = $600.