What this calculator does

DocketMath’s Closing Date Prorations Calculator helps you estimate proration amounts tied to a contract’s closing date in Washington (US-WA). In practice, “proration” often shows up when costs or obligations must be allocated between two time periods—commonly the date the agreement is formed and the date ownership or responsibility begins, or the date one party takes possession versus another.

Because prorations depend heavily on the exact closing date, the calculator is designed to:

• Take your closing date (and related dates) as primary inputs.
• Compute time-weighted allocations (for example, day-by-day splits) so the prorated amount aligns with the calendar.
• Keep an audit trail of how each output was derived, so you can double-check the math quickly.

This guide also ties the calculator’s logic to Washington’s governing limitation period rules where relevant to scheduling or time-based calculations. For Washington, the baseline limitation period is generally 5 years under RCW 9A.04.080, subject to specific exceptions (notably certain shorter periods).

Key Washington timing rule used by the tool logic (where applicable)

Washington’s limitation period framework is anchored in RCW 9A.04.080:

• General rule: 5 years under RCW 9A.04.080
• Exception P1: RCW 9A.04.080 — 5 years — exception P1
• Exception V1: RCW 9A.04.080(1)(j) — 3 years — exception V1
• Exception V2: null — 3 years — exception V2

In other words, if your prorations involve choosing between timelines that may be governed by a 5-year vs. 3-year clock, the calculator can be aligned with the applicable limitation window based on the exception you select. (You’ll still want to confirm which exception actually matches your situation.)

Output types you can expect

Depending on how you enter inputs, the calculator typically produces:

• Number of days included in each relevant period
• Percent share for each period
• Prorated amount(s) based on a total charge (or total obligation)
• A summary that you can use to document your computation steps

When to use it

Use the DocketMath closing-date prorations workflow when your numbers hinge on day-level timing and the contract or settlement mechanics require dividing a cost or responsibility across dates.

Common triggers include:

• Closing date-driven expense allocation: Taxes, HOA-style assessments, insurance premiums, interest accruals, or other charges that start/stop based on closing.
• Two-party timeline splits: Situations where one party benefits from a service or resource during one portion of the month/period and another party during the remainder.
• Backdating or forward-dating risk checks: When a stated closing date is different from the date the agreement was executed, and you need the prorated financial effect.

Additionally, if your proration framework is connected to a time-based limitation window, Washington’s rule in RCW 9A.04.080 may matter to your planning. Specifically:

• Baseline calculations can map to a 5-year period (RCW 9A.04.080)
• Some scenarios may map to a 3-year period under RCW 9A.04.080(1)(j) (Exception V1) or another 3-year exception (Exception V2)

Step-by-step example

Below is a concrete walkthrough showing how closing date changes the proration.

We’ll assume the total charge is a monthly amount that must be split across two time periods: Period A (before closing) and Period B (after closing). The calculator handles the day-count approach so you don’t have to.

Scenario setup

• Contract/assessment total: $900
• Billing period: April 1, 2026 through April 30, 2026 (30 days)
• Closing date: April 14, 2026
• Goal: allocate the $900 prorated between:

  • Period A: April 1–April 13 (the day before closing)
  • Period B: April 14–April 30 (from closing onward)

Step-by-step inputs

1. Open the tool: /tools/closing-date-prorations
   (If you’re building a workflow, you can also cross-check related deadlines with the general calculators at /tools.)

2. Enter the dates:

   • Start of allocation period: 2026-04-01
   • Closing date: 2026-04-14
   • End of allocation period: 2026-04-30

3. Enter the total charge:

   • Total for the allocation period: $900

4. Select the proration basis (if the tool offers a choice):

   • Day-by-day / calendar day proration (typical default)

5. If the tool asks for a limitation-window selector tied to timing rules:

   • Choose the appropriate limitation window only if your calculation depends on it.
   • Washington timing baseline rules you may encounter:

     • 5 years: RCW 9A.04.080
     • 3 years: RCW 9A.04.080(1)(j) (Exception V1) or other 3-year exception (Exception V2)

For purely financial prorations (day splits of a monthly charge), limitation selection usually won’t change the arithmetic; it matters when the tool is used to align computations to limitation clocks.

Compute the day split (what the calculator is doing)

• Total days in April 2026 allocation period: 30
• Days in Period A (April 1–13): 13 days
• Days in Period B (April 14–30): 17 days

Percentages:

• Period A: 13 / 30 = 43.333…%
• Period B: 17 / 30 = 56.666…%

Amounts:

• Period A prorated amount: $900 × 0.43333… = $390.00
• Period B prorated amount: $900 × 0.56666… = $510.00

Interpreting the output

A typical tool output summary you should look for:

• Days before closing: 13
• Days after closing: 17
• Prorated charge (before): $390.00
• Prorated charge (after): $510.00
• Total check: should sum to $900.00

Common scenarios

Below are practical variations that change proration results, along with the decisions you should make in the calculator.

Scenario 1: Closing date moves by 1–2 days

Assume:

• Total monthly charge: $900
• Allocation month: **April (30 days)
• Closing date shift:

  • From April 14 → April 16

Day-count effect:

• If closing shifts later, Period A gains days and Period B loses days.
• Specifically:

  • April 14 closing: Period A = 13 days, Period B = 17 days
  • April 16 closing: Period A = 15 days, Period B = 15 days

Estimated split:

• New Period A: 15/30 = 50% → $450
• New Period B: 15/30 = 50% → $450

Even small date changes can swing amounts meaningfully because proration is calendar-day based.

Scenario 2: Billing period isn’t a full month

Sometimes charges cover a custom range (e.g., “from March 10 through April 9”). In that case:

• The tool needs:

  • allocation period start date
  • closing date
  • allocation period end date
• You should confirm the date range matches the contract’s billing schedule—not just “the month.”

Checkbox checklist before running:

Scenario 3: Multi-charge prorations

If you have multiple charges (e.g., insurance + HOA assessment), you can:

• Run the calculator separately for each total, or
• Enter a combined total if the allocation period and closing date are identical for every line item

If line items have different start/stop rules, keep them separate to avoid blending incompatible timelines.

Scenario 4: Timing windows for time-based rules (RCW 9A.04.080)

While prorations are typically financial allocations, some workflows use limitation windows to model timelines and deadlines. Washington’s general rule and exceptions include:

• 5-year limitation period: RCW 9A.04.080
• 3-year exceptions:

  • RCW 9A.04.080(1)(j) (Exception V1)
  • Another 3-year exception (Exception V2)

Practical impact on calculator-driven workflows:

• A selected exception may change the computed “end date” for a time window.
• That, in turn, can shift which dates you choose as “included” in certain calculations.

Tips for accuracy

• **

Sources and references

Start with the primary authority for Washington and confirm the effective date before relying on any output. If the rule has been amended, update the inputs and rerun the calculation.

• Primary authority reference

Related reading

• Closing Date Prorations Calculator Guide for Alabama
• Closing Date Prorations Calculator Guide for Arizona
• Closing Date Prorations Calculator Guide for California