Transparent math for everyday money
A free proration calculator for rent, salaries, subscriptions, and utilities, built so you always know exactly what you owe and why.
Why We Built This
Proration math trips people up constantly, not because it's hard, but because there are too many ways to get a different answer depending on how you count the days. We've seen tenants handed incorrect bills, HR departments make payroll errors, and subscription services quietly charge more than they should.
This calculator gives you a single, defensible number based on the standard daily-rate method, the same approach used by accountants, property managers, and HR professionals across the U.S. Enter your billing amount, your period type, and the days you actually used. You get the prorated charge, the daily rate, and enough detail to verify the math yourself.
No sign-up. No ads on the calculator. No paywall. Just the math.
The Proration Standard
Our formula, (Total Amount ÷ Total Days) × Days Used, follows the AICPA-endorsed daily-rate method. For monthly periods we use 30 days, consistent with the majority of U.S. lease agreements and the Uniform Residential Landlord and Tenant Act (URLTA).
What We Cover
Monthly and annual rent proration, salary proration for partial pay periods, subscription billing adjustments, and utility splits. If a billing amount needs to be split across fewer days than its full cycle, this tool handles it.
Accuracy You Can Check
We show you the daily rate and all intermediate numbers so you can verify the calculation yourself. Our results match what a licensed accountant would produce using the same inputs. We note where local laws may affect the outcome.
Our Sources
We reference the AICPA, Nolo's tenant rights resources, the Consumer Financial Protection Bureau (CFPB), and the Uniform Residential Landlord and Tenant Act. All source citations appear on the calculator page.
How We Research and Update Our Calculations
Every formula on this site is reviewed against published accounting standards and legal resources before going live. When laws change, like state-level updates to landlord-tenant statutes, we update the methodology notes on the relevant pages.
Our blog covers proration topics in detail: how the 30-day vs. calendar-month methods differ, how HR departments handle partial pay periods, and what tenants should know before signing a lease. All articles are written by our research team and cross-checked against primary sources.
Disclaimer: Results from this calculator are estimates for informational purposes. Actual prorated amounts may vary depending on your specific lease terms, state laws, and your landlord's or employer's calculation method. When dealing with significant sums, always confirm the calculation in writing with the relevant party.
Get in Touch
Found a calculation error, have a question about proration, or want to suggest a new feature?
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